Pressure-sensitive touch panel

ABSTRACT

A device for combined capacitance and pressure measurements includes a plurality of first input/output terminals for a projected capacitance touch panel wherein the projected capacitance touch panel includes a layer of piezoelectric material disposed between a plurality of sensing electrodes and a common electrode. The device also includes a plurality of second input/output terminals for a capacitive touch controller. The device also includes a plurality of separation stages, each separation stage connecting one first input/output terminal to a corresponding second input/output terminal, and each separation stage includes a first frequency-dependent filter for filtering signals between respective first and second input/output terminals. The device also includes at least one amplification stage, each amplification stage having at least one input and an output configured to provide an amplified signal, wherein the number of amplification stages is less than or equal to the number of separation stages and each amplification stage input is connected to one or more of the first input/output terminals through the respective separation stage(s) Each amplification stage or each separation stage includes a second frequency-dependent filter for filtering signals between the respective first input/output terminal and an amplification stage input. Each first frequency-dependent filter is configured to pass signals from the capacitive touch controller and each second frequency-dependent filter is configured to attenuate signals from the capacitive touch controller.

FIELD OF THE INVENTION

The present invention relates to a touch panel for combined capacitiveand pressure sensing.

BACKGROUND

Resistive and capacitive touch panels are used as input devices forcomputers and mobile devices. One type of capacitive touch panel,projected capacitance touch panels, is often used for mobile devicesbecause an exterior layer may be made of glass, providing a hard surfacewhich is resistant to scratching. An example of a projected capacitancetouch panel is described in US 2010/0079384 A1.

Projected capacitance touch panels operate by detecting changes inelectric fields caused by the proximity of a conductive object. Thelocation at which a projected capacitance touch panel is touched isoften determined using an array or grid of capacitive sensors. Althoughprojected capacitance touch panels can usually differentiate betweensingle-touch events and multi-touch events, they suffer the drawback ofnot being able to sense pressure. Thus, projected capacitance touchpanels tend to be unable to distinguish between a relatively light tapand a relatively heavy press. A touch panel that can sense pressure canallow a user to interact with a device in new ways by providingadditional information to simply position of a touch.

Different approaches have been proposed to allow a touch panel to sensepressure. One approach is to provide capacitive sensors which include agap whose size can be reduced by applied pressure, so as to produce ameasureable difference in the mutual capacitance. For example, US2014/043289 A describes a pressure sensitive capacitive sensor for adigitizer system which includes an interaction surface, at least onesensing layer operable to sense interaction by mutual capacitivesensing, and an additional layer comprising resilient properties andoperable to be locally compressed responsive to pressure locally appliedduring user interaction with the capacitive sensor. However, the needfor a measurable displacement can make it more difficult to use a glasstouch surface and can cause problems with material fatigue afterrepeated straining.

Other pressure sensitive touch panels have proposed using one or morediscrete force sensors supporting a capacitive touch panel, such thatpressure applied to the capacitive touch panel is transferred to one ormore sensors located behind the panel or disposed around the periphery.For example, US 2013/0076646 A1 describes using strain gauges with aforce sensor interface which can couple to touch circuitry. WO2012/031564 A1 describes a touch panel including a first panel, a secondpanel, and a displacement sensor sandwiched between the first panel andthe second panel. The displacement sensors, such as capacitive or piezoresistive sensors are placed around the edge of the second panel.However, it can be difficult to distinguish the pressure of multipletouches using sensors located behind a touch panel or disposed aroundthe periphery.

Other pressure sensitive touch panels have been proposed which attemptto combine capacitive touch sensing with force sensitive piezoelectriclayers. For example, WO 2009/150498 A2 describes a device including afirst layer, a second layer, a third layer, a capacitive sensingcomponent coupled to the first layer, and a force sensing componentcoupled to the first layer and the third layer and configured to detectthe amount of force applied to the second layer. WO 2015/046289 A1describes a touch panel formed by stacking a piezoelectric sensor and anelectrostatic sensor. The piezoelectric sensor is connected to apressing force detection signal generation unit, and the electrostaticsensor is connected to a contact detection signal generation unit.However, systems which use separate electrodes and/or separateelectronics to sense changes in capacitance and pressures can make atouch panel more bulky and expensive. Systems in which electrodes aredirectly applied or patterned onto a piezoelectric film can be morecomplex and expensive to produce.

SUMMARY

The present invention seeks to provide an improved capacitive touchpanel. According to a first aspect of the invention there is provided adevice including a number of first input/output terminals for aprojected capacitance touch panel, wherein the projected capacitancetouch panel includes a layer of piezoelectric material disposed betweena plurality of sensing electrodes and a common electrode. The devicealso includes a plurality of second input/output terminals for acapacitive touch controller. The device also includes a plurality ofseparation stages, each separation stage connecting one firstinput/output terminal to a corresponding second input/output terminal,and each separation stage including a first frequency-dependent filterfor filtering signals between respective first and second input/outputterminals. The device also includes at least one amplification stage,each amplification stage having at least one input and an outputconfigured to provide an amplified signal, wherein the number ofamplification stages is less than or equal to the number of separationstages and each amplification stage input is connected to one or more ofthe first input/output terminals through the respective separationstage(s). Each amplification stage or each separation stage includes asecond frequency-dependent filter for filtering signals between therespective first input/output terminal and an amplification stage input.Each first frequency-dependent filter is configured to pass signals fromthe capacitive touch controller and each second frequency-dependentfilter is configured to attenuate signals from the capacitive touchcontroller.

Thus, pressure and capacitance measurements may be performed using asingle set of electrodes. This allows pressure and capacitancemeasurements to be integrated into a touch panel and control systemwithout substantially increasing the complexity of a touch panel. Asingle signal including both pressure and capacitance information may beprocessed in a way which may he readily integrated with existingprojected capacitance touch panels and capacitive touch controllers.

Each first frequency dependent filter may comprise at least oneband-pass filter and each second frequency dependent filter may compriseat least one low-pass filter. The first frequency-dependent filter maycomprise at least one band-pass filter and the secondfrequency-dependent filter may comprise at least one band-stop filter.The first frequency-dependent filter may comprise a high-pass filter andthe second frequency-dependent filter may comprise a low-pass filter.Each band-pass filter may be a notch or comb filter. Each band-stopfilter may be a notch or comb filter. Filters may comprise active filtercircuits. Filters may comprise passive filter circuits. Filters maycomprise a single stage. Filters may comprise multiple stages. Filtersmay comprise filter circuits selected from the group consisting ofButterworth filters, Chebyshev filters, Gaussian filters and Besselfilters.

The second frequency dependent filter may have a low-frequency cut-offconfigured to reject a pyroelectric response of the layer ofpiezoelectric material in the touch panel. The low frequency cut-off maybe at least 7 Hz. The second frequency dependent filter may have alow-frequency cut-off configured to reject a mains power distributionfrequency. The second frequency dependent filter may include a notchfilter centred at a mains power distribution frequency. The mains powerdistribution frequency may be 50 Hz, 60 Hz, at least 100 Hz, at least200 Hz or at least 400 Hz.

The second frequency-dependent filters may be configured such that theamplitude of the amplified signal from each amplification stage outputis dependent upon a pressure applied to the projected capacitance touchpanel proximate to the sensing electrode(s) connected to thecorresponding first input/output terminal(s).

Each amplification stage may be connected to one first input/outputterminal through one separation stage. Each amplification stage may beconnected to a two or more of the first input/output terminals throughrespective separation stages.

Each amplification stage may include a virtual earth amplifier toprovide the amplified signal. Each amplification stage may include anintegrating amplifier to provide the amplified signal. Eachamplification stage may include a charge amplifier to provide theamplified signal.

The plurality of separation stages and the plurality of amplificationstages may be connected by a resistance network. The plurality ofseparation stages and the plurality of amplification stages may beconnected using one or more multiplexers.

The device may further include a common terminal for receiving biassignals from the capacitive touch controller. Each separation stage mayfurther include an additional first frequency-dependent filter, and areference resistance and a reference capacitance connected in series,each separation stage configured to connect the respective secondinput/output terminal to the common terminal through the referenceresistance and capacitance, the additional first frequency-dependentfilter for filtering signals between the respective second input/outputterminal and the common terminal. Each amplification stage may be adifferential amplification stage having a first amplification stageinput connected to one or more of the first input/output terminalsthrough the respective separation stage(s) and a second amplificationstage input connected to the common terminal through the referenceresistance and reference capacitance of the respective separationstage(s). In dependence upon each separation stage including a secondfrequency-dependent filter, each separation stage may further include anadditional second frequency-dependent filter for filtering signalsbetween the respective second amplification stage input first terminaland the common terminal.

Thus, capacitance measurements may be combined with differentialamplification of pressure signals to improve the signal to noise ratioof the amplified signals.

The first frequency dependent filter may be a capacitance.

Each amplification stage may include a second frequency dependentfilter, and each second frequency dependent filter may be a feedbacknetwork(s) and one or more operational amplifiers. A feedback networkmay be a resistance-capacitance network.

The device may further include a third terminal. The device may furtherinclude a pressure signal processing module having a plurality of inputsand an output, each input connected to a corresponding amplificationstage output, and the output connected to the third terminal. Thepressure signal processing module may be configured to receive theamplified signals, to calculate pressure values in dependence upon theamplified signals, and to provide an output comprising pressure valuesto the third terminal.

The device may further include a plurality of third terminals, eachthird terminal connected to a corresponding amplification stage output.

The device may further include a capacitive touch controller having aplurality of electrode monitoring ports and a common output port, eachelectrode monitoring port connected to a corresponding secondinput/output terminal, and the common output port for providing biassignals to a common electrode of the projected capacitance touch panel.The capacitive touch controller may be configured to send and/or receivesignals to and/or from sensing electrodes of the projected capacitancetouch panel via the respective signal separation stages, to calculatecapacitance values in dependence upon the sent and/or received signals,and to provide an output comprising capacitance values.

An apparatus may be provided which includes the device and a pressuresignal processing module having a plurality of inputs and an output,each input connected to a corresponding third terminal of the device.The pressure signal processing module may be configured to receive theamplified signals, to calculate pressure values in dependence upon theamplified signals, and to provide an output comprising pressure values.

The pressure signal processing module may be housed in a separatepackage to the device and be connected to the device.

An apparatus may be provided which includes the device, the pressuresignal processing module and a capacitive touch controller having aplurality of electrode monitoring ports and a common output port. Eachelectrode monitoring port may be connected to a corresponding secondinput/output terminal of the device, and the common output port may befor providing bias signals to a common electrode of the projectedcapacitance touch panel. The capacitive touch controller may beconfigured to send and/or receive signals to and/or from sensingelectrodes of the projected capacitance touch panel via the respectivesignal separation stages, to calculate capacitance values in dependenceupon the sent and/or received signals, and to provide an outputcomprising capacitance values.

The capacitive touch controller may be housed in a separate package tothe device and may be connected to the device.

The capacitive touch controller may be configured to determine aself-capacitance of a sensing electrode of the touch panel. Thecapacitive touch controller may be configured to determine a mutualcapacitance between a pairing of sensing electrodes of the touch panel.The capacitive touch controller may measure the self-capacitance of eachsensing electrode sequentially. The capacitive touch controller maymeasure the self-capacitance of sensing electrodes simultaneously. Thecapacitive touch controller may measure the mutual capacitance for eachpairing of sensing electrodes sequentially. Each electrode monitoringport connects to one second input/output terminal. The capacitive touchcontroller may be a controller for a capacitive touch panel which doesnot include a layer of piezoelectric material.

A touch panel system may be provided which includes the device or theapparatus including the device, and which further includes a touchpanel. The touch panel may include a layer structure including one ormore layers, each layer extending perpendicularly to a thicknessdirection, the one or more layers including a layer of piezoelectricmaterial, the layer structure having first and second opposite faces,and the layer(s) arranged between the first and second faces such thatthe thickness direction of each layer is perpendicular to the first andsecond faces. The touch panel may also include a plurality of firstsensing electrodes disposed on the first face, each first sensingelectrode connected to a corresponding first input/output terminal. Thetouch panel may also include a common electrode disposed on the secondface for receiving a bias signal from a capacitive touch controller. Independence upon the device or the apparatus including a common terminal,the common electrode may be connected to the common terminal. Independence on the device or the apparatus including a capacitive touchcontroller, the common output port of the capacitive touch controllermay be connected to the common electrode.

The layer structure may include one or more dielectric layers stackedbetween the layer of piezoelectric material and the first thee of thelayer structure. The layer structure may include one or more dielectriclayers stacked between the second face of the layer structure and thelayer of piezoelectric material.

The common electrode may be a region of conductive material arranged ina grid.

Thus, the common electrode may be located between the sensing electrodesand a user without screening electrostatic interactions

The plurality of first electrodes may be a plurality of conductive padsdisposed on the first face in an array.

The touch panel may further include a plurality of second sensingelectrodes disposed overlying the first face of the layer structure andarranged such that the layer structure is between the plurality ofsecond sensing electrodes and the common electrode. Each of the secondsensing electrodes may be connected to a corresponding firstinput/output terminal. Each of the first input/output terminals may beconnected to one first sensing electrode or one second sensingelectrode.

Each first sensing electrode may extend in a first direction and theplurality of first sensing electrodes may be arrayed spaced apartperpendicular to the first direction. Each second sensing electrode mayextend in a second direction and the plurality of second sensingelectrodes may be arrayed spaced apart perpendicular to the seconddirection. The first and second directions may be different.

The touch panel may further include a second layer structure includingone or more dielectric layers, each dielectric layer extendingperpendicularly to a thickness direction, the second layer structurehaving third and fourth opposite faces, the dielectric layers arrangedbetween the third and fourth faces such that the thickness direction ofeach dielectric layer is perpendicular to the third and fourth faces.The plurality of second sensing electrodes may be disposed on the thirdface of the second layer structure and the fourth face of the secondlayer structure may contact the plurality of first sensing electrodes.

The plurality of second sensing electrodes may be disposed on the firstface of the layer structure. Each first sensing electrode may be acontinuous conductive region and each second sensing electrode may be aplurality of conductive regions electrically connected to one another byjumpers, each jumper spanning a conductive region forming a portion ofone of the first sensing electrodes.

The touch panel may include a plurality of separated common electrodes.The touch panel may further include a plurality of second sensingelectrodes disposed on the second face of the layer structure. Eachsecond sensing electrode may be connected to a respective firstinput/output terminal. Each first sensing electrode may extend in afirst direction and the plurality of first sensing electrodes may bearrayed spaced apart perpendicular to the first direction. Eachseparated common electrode may extend in a second direction and theplurality of separated common electrodes may be arrayed spaced apartperpendicular to the second direction. Each second sensing electrode mayextend in a second direction and the plurality of second sensingelectrodes may he arrayed spaced apart perpendicular to the seconddirection. The second sensing electrodes may be arranged parallel to andinterleaved with the plurality of separated common electrodes. The firstand second directions may be different. The first and second directionsmay be substantially perpendicular. The first and second directions maymeet at an angle of more than 30 and less than 90 degrees.

The capacitive touch controller may be configured to determine aself-capacitance of a first or second sensing electrode of the touchpanel. The capacitive touch controller may be configured to determine amutual capacitance between a pairing of first and second sensingelectrodes of the touch panel. The capacitive touch controller maymeasure the self-capacitance of the first and second sensing electrodessequentially. The capacitive touch may measure the self-capacitance ofthe first and second sensing electrodes simultaneously. The capacitivetouch controller may measure the mutual capacitance for each pairing offirst and second sensing electrodes sequentially. Each electrodemonitoring port connects to one second input/output terminal. Thecapacitive touch controller way he a controller which is suitable foruse in a capacitive touch panel which does not include a layer ofpiezoelectric material.

According to a second aspect of the invention there is provided aportable electronic device including the device, apparatus or touchpanel system.

According to a third aspect of the invention there is provided aportable electronic device including the device, apparatus or touchpanel system and a signal processor arranged to receive the pressurevalues and/or capacitance values. The signal processor may be configuredto employ correlated double sampling methods so as to improve signal tonoise ratio of the pressure values and/or capacitance values.

The signal processor may be configured to treat the pressure valuesand/or the capacitance values as image data. Each pressure value and/oreach capacitance value may correspond to one pixel value of the imagedata. The signal processor may be configured to treat the pressurevalues as a pressure value image and to treat the capacitance values asa capacitance value image.

The touch panel may overlie a display screen. The touch panel may beintegrated into a display screen.

According to a fourth aspect of the invention there is provided a methodincluding transmitting and filtering, using a first frequency-dependentfilter, signals between a capacitive touch controller and a sensingelectrode of a projected capacitance touch panel which comprises a layerof piezoelectric material disposed between a plurality of sensingelectrodes and a common electrode. The method also includes filtering,using a second frequency-dependent filter, signals between the sensingelectrode of the projected capacitance touch panel and an amplificationstage input to produce a filtered signal. The method also includesamplifying the filtered signal to produce an amplified signal. Eachfirst frequency-dependent filter is configured to pass signals from thecapacitive touch controller and each second frequency-dependent filteris configured to attenuate signals from the capacitive touch controller.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings in which:

FIG. 1 illustrates a device and touch sensor for combined capacitanceand pressure measurements;

FIG. 2 illustrates a second device and a second touch sensor forcombined capacitance and pressure measurements;

FIG. 3 shows a schematic block diagram of an electronic deviceincorporating a device and a touch panel for combined capacitance andpressure measurements;

FIG. 4 shows a simplified cross-section of a first touch panel forcombined capacitance and pressure measurements;

FIG. 5 illustrates a first touch panel system for combined capacitanceand pressure measurements;

FIG. 6 shows a layout of sensing electrodes for a second touch panel forcombined capacitance and pressure measurements;

FIG. 7 shows a layout of sensing electrodes for a third touch panel forcombined capacitance and pressure measurements;

FIG. 8 shows a layout for a patterned common electrode for use in atouch panel for combined capacitance and pressure measurements;

FIG. 9 illustrates using interpolation to infer a location and/or apressure of a user interaction for a touch panel;

FIG. 10 illustrates an implementation of the first touch panel systememploying differential amplification;

FIG. 11 illustrates an example of a circuit for implementing adifferential signal separation stage shown in FIG. 10;

FIG. 12 illustrates an example of a circuit for implementing adifferential amplification stage shown in FIG. 10;

FIGS. 13A to 13F illustrate measuring the self-capacitance of a sensingelectrode when no user interaction is occurring;

FIGS. 14A to 14I illustrate measuring self-capacitance of a sensingelectrode combined with measuring the pressure applied by a userinteraction;

FIG. 15 illustrates implementing mutual capacitance measurements betweena pair of sensing electrodes using the first touch panel system;

FIGS. 16A to 16F illustrate measuring a mutual-capacitance between apair of sensing electrodes when no user interaction is occurring;

FIGS. 17A to 17F illustrate measuring a mutual-capacitance between apair of sensing electrodes when there is a light user interactionproximate to the sensing electrodes;

FIGS. 18A to 18F illustrate measuring a mutual-capacitance between apair of sensing electrodes combined with measuring a pressure applied bya user interaction proximate to the sensing electrodes;

FIG. 19 illustrates implementing the first touch panel system shown inFIG. 5 using an equal numbers of separation and amplification stages;

FIG. 20 illustrates implementing the first touch panel system shown inFIG. 5 using an unequal numbers of separation and amplification stages;

FIG. 21 illustrates an implementation of the first touch panel systememploying single input amplification;

FIG. 22 shows a simplified cross-section of a fourth touch panel forcombined capacitance and pressure measurements;

FIG. 23 illustrates a second touch panel system for combined capacitanceand pressure measurements;

FIGS. 24 to 31 show simplified cross-sections of first to eighth displaystack-ups for providing touch panels for combined capacitance andpressure measurements; and

FIGS. 32 to 39 show simplified cross-sections of first to eighthembedded stack-ups for providing touch panels for combined capacitanceand pressure measurements;

FIG. 40 is a plan view of an arrangement of electrodes for a fifth touchpanel for combined capacitive and pressure sensing; and

FIG. 41 is a cross-sectional view of the touch panel shown in FIG. 40.

DETAILED DESCRIPTION

In the following description, like parts are denoted by like referencenumerals.

Combined Self-Capacitance and Pressure Measurements

FIG. 1 illustrates a device 1 and touch sensor 4 for combinedcapacitance and pressure measurements.

Referring to FIG. 1, a device 1 for combined capacitance and pressuremeasurements includes a signal separation stage 2 and an amplificationstage 3. The device 1 is connected to a touch sensor 4, a capacitivetouch controller 5 and a pressure signal processing module 6. The device1 allows capacitance and pressure measurements to be made from the touchsensor 4 concurrently using one pair of electrodes.

The first touch sensor 4 includes a layer structure 7 having a firstface 8 and a second, opposite, face 9, a first sensing electrode 10 anda common electrode 11. The layer structure 7 includes one or morelayers, including at least a layer of piezoelectric material 12. Eachlayer included in the layer structure 7 is generally planar and extendsin first and second directions x, y which are perpendicular to athickness direction z. The one or more layers of the layer structure 7are arranged between the first and second faces 8, 9 such that thethickness direction z of each layer of the layer structure 7 isperpendicular to the first and second faces 8, 9. The first sensingelectrode 10 is disposed on the first face of the layer structure 7, andthe common electrode 11 is disposed on the second face 9 of the layerstructure 7.

Preferably, the piezoelectric material is a piezoelectric polymer, forexample a suitable fluoropolymer such as polyvinylidene fluoride (PVDF).However, the piezoelectric material may alternatively be a layer of apiezoelectric ceramic such as lead zirconate titanate (PZT). Preferably,the first and second electrodes are indium tin oxide (ITO) or indiumzinc oxide (IZO). However, the first and second electrodes 10, 11 may beconductive polymers such as polyaniline, polythiphene, polypyrrole orpoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). Thefirst and second electrodes 10, 11 may be metal films such as aluminium,copper, silver or other metals suitable for deposition and patterning asa thin film. The first and second electrodes may be formed from a metalmesh; nanowires, optionally silver nanowires; graphene; and carbonnanotubes.

The device 1 includes a first input/output terminal 13 for connecting tothe touch sensor 4 and a second input/output terminal 14 for connectingto the capacitive touch controller 5. The signal separation stage 2includes a first, capacitance signal filter 15. The signal separationstage 2 connects the first input/output terminal 13 to the secondinput/output terminal 14 via the capacitance signal filter 15. Thecapacitance signal filter 15 filters signals between the secondinput/output terminal 14 and the first input/output terminal 13. Thesignal separation stage 2 also connects the amplification stage 3 to thefirst input/output terminal 13. Signals between the first input/outputterminal 13 and the amplification stage 3 are not filtered by thecapacitance signal filter 15.

The amplification stage 3 is connected to the first input/outputterminal 13 through the signal separation stage 2. The amplificationstage 3 includes a second, pressure signal filter 16 and an amplifier17. The pressure signal filter 16 receives a touch sensor signal 18 andfilters it to produce a pressure signal 19. The amplifier 17 receivesthe pressure signal 19 and amplifies it to output an amplified signal20. The amplifier 17 may provide additional frequency dependentfiltering. When the amplifier 17 is a differential amplifier, theamplifier 17 may receive an additional input (FIG. 10). The amplifier 17is preferably a virtual earth amplifier such as, for example, a chargeamplifier.

Alternatively, the pressure signal filter 16 may be integrated as asingle unit with the amplifier 17 such as, for example, an operationalamplifier and a resistance-capacitance feedback network. In this case,the amplifier 17 receives the touch sensor signal 18 directly and theamplified signal 20 is based on the touch sensor signal 18.

Alternatively, the pressure signal filter 16 may be included in thesignal separation stage 2 instead of the amplification stage 3. When thepressure signal filter 16 is included in the signal separation stage 2,the pressure signal filter 16 filters signals between the firstinput/output terminal 13 and the amplification stage 3. Signals betweenthe first and second input/output terminals 13, 14 are not filtered bythe pressure signal filter 16.

The pressure signal filter 16 and/or the amplifier 17 may have alow-frequency cut-off configured to reject a pyroelectric response ofthe layer of piezoelectric material 12. The low frequency cut-off maytake a value between 1 Hz and 7 Hz. The pressure signal filter 16 and/orthe amplifier 17 may include a notch filter configured to reject a mainspower distribution frequency, for example, 50 Hz or 60 Hz.Alternatively, the mains power notch filter may be a separate filterstage (not shown) disposed before or after the pressure signal filter 16and/or the amplifier 17.

The capacitive touch controller 5 is, in general, a conventionalcapacitive touch controller capable of measuring the self-capacitance ofan electrode. For example, the capacitive touch controller may be acommercially available touch controller such as an Atmel® MXT224 touchcontroller. The capacitive touch controller 5 outputs a capacitancemeasurement signal 21 which drives the sensing electrode 10 through thesignal separation stage 2. The capacitance signal filter 15 has afrequency response which passes the capacitance measurement signals 21produced by the capacitive touch controller 5 without attenuation, orwith minimal attenuation. The capacitance touch controller 5 is alsoconnected to the common electrode 11 of the touch sensor 4 to output abias signal 22 to the common electrode 11. During measurements of theself-capacitance of the sensing electrode 10, the bias signal 22 is thesubstantially the same as the capacitance measurement signal 21, inorder to remove the influence of mutual capacitance between the sensingelectrode 10 and the common electrode 11. The self-capacitance of thesensing electrode 10, i.e. the capacitance between the sensing electrode10 and earth, is determined by the capacitive touch controller 5 usingan internal charge amplifier (not shown). In this way, the capacitancetouch controller 5 calculates a capacitance value in dependence uponcapacitance measurement signals 21, and provides an output comprisingcapacitance values 23.

The specific method for measuring the self-capacitance of the sensingelectrode 10, and the specific waveforms of the capacitance measurementsignals 21 and bias signal 22, depend on the particular capacitive touchcontroller 5 used. However, any capacitive touch controller 5 may beused with the device 1 by adjusting the bandwidth of the capacitancesignal filter 15 to pass the capacitance measurement signals 21 producedby a particular capacitive touch controller 5.

The touch sensor signal 18 may differ from the capacitance measurementsignal 21 in response to a user interaction with the touch sensor 4, orwith a layer of material overlying the touch sensor 4, which produces apiezoelectric response from the layer of piezoelectric material 12. Auser interaction refers to a user touching or pressing a touch sensor 4,a touch panel 36 (FIG. 5) or a layer of material overlying either, e.g.cover lens 46 (FIG. 24). A user interaction may involve a user's digitor a stylus (whether conductive or not). A touch interaction may includea user's digit or conductive stylus being proximate to a touch sensor 4or touch panel 36 (FIG. 5) without direct physical contact or withoutapplying significant pressure. A press interaction involves a userpressing the touch sensor 4 or touch panel 36 (FIG. 5) with sufficientforce to cause straining of the layer of piezoelectric material 12 andgeneration of a piezoelectric response.

The layer of piezoelectric material 12 is poled such that the layer ofpiezoelectric material 12 becomes polarised with a polarisation P inresponse to straining caused by a user interaction which appliessufficient force. The polarisation P of the layer of piezoelectricmaterial results in a corresponding charge Q_(piezo)(t) being developedbetween the common electrode 11 and the sensing electrode(s) 10. Thelayer of piezoelectric material I should be arranged and poled such thatthe charge Q_(piezo)(t) developed between the common electrode 11 andthe sensing electrode(s) 10 is sufficient to produce a detectableresponse at a location proximate to the user interaction. The strainingwhich produces the polarisation P may result from a compression or atension. The straining which produces the polarisation P may be anin-plane stretching of the piezoelectric material layer 12. Intimatecontact between the layer of piezoelectric material 12 and theelectrodes 10, 11 is not required. Generally, a greater straining of thelayer of piezoelectric material 12 (caused by a more forceful userinteraction) will result in a greater polarisation P, and acorrespondingly larger magnitude of the charge difference ΔQ_(piezo)produced between the electrodes 10, 11.

In this way, the touch sensor signal 18 is approximately a superpositionof a capacitance measurement signal 21 and a piezoelectric responseI_(piezo)(t), which is the current associated with the chargeQ_(piezo)(t). The piezoelectric response I_(piezo)(t) may be integratedand amplified to determine the charge Q_(piezo) produced in response toa user interaction. Because the capacitance signal filter 15 is adaptedto pass the capacitance measurement signals 21, the capacitive touchcontroller 5 may communicate with a the touch sensor 4 and measure theself-capacitance of the sensing electrode 10 with no, or minimal,interference from the device 1 and the piezoelectric responseI_(piezo)(t) of the layer of piezoelectric material 12. In this way, acapacitive touch controller 5 suitable for use with a conventionalprojected capacitance touch panel can be used with the device 1. Thepressure signal filter 16 is adapted to reject, or at least attenuate,capacitance measurement signals 21. In this way, the amplified signal 20may be based on the piezoelectric response I_(piezo)(t) produced bystraining the layer of piezoelectric material 12.

The separation of capacitance measurements signals 21 and pressuresignals 19 is possible because the frequency bandwidth of thepiezoelectric response I_(piezo)(t) to user interactions typically spansa frequency bandwidth which may be significantly below the frequencybandwidth of capacitance measurements signals 21. The capacitancemeasurement signals 21 may typically be selected to have a basicfrequency, f_(d), of greater than or equal to 10 kHz, greater than orequal to 20 kHz, greater than or equal to 50 kHz, greater than or equalto 100 kHz or up to 500 kHz. The capacitance measurement signals 21 mayinclude multiple frequency components, such as, for example, step,square or triangular waveforms, or may be provided with a narrowfrequency band or even a single frequency signal, such as a sinusoidalsignal.

By contrast, the piezoelectric response I_(piezo)(t) typically includesa broadband frequency content spanning a range from several Hz toseveral hundreds or thousands of Hz. For example, the piezoelectricresponse I_(piezo)(t) may include frequency components between 1 Hz and1 kHz. This is mainly because the piezoelectric response I_(piezo)(t)arises from user interactions by a human user, and partly because a timeconstant of the piezoelectric response I_(piezo)(t) may be influenced asexplained hereinafter.

In this way, the capacitance signal filter 15 may be adapted to pass thecapacitance measurement signals 21 having relatively higher frequencycontent, and the pressure signal filter 16 may be adapted so that thepressure signal 19 is substantially based on the relatively lowerfrequency piezoelectric response I_(piezo)(t). For example, thecapacitance signal filter 15 may be a high-pass filter and the pressuresignal filter 16 may be a low-pass filter. In this way, the amplitude ofthe amplified signal 20 is dependent upon a pressure applied to thelayer of piezoelectric material 12 by a user interaction. The pressuresignal processing module 6 receives the amplified signals 20, determinespressure values 24 and provides the pressure values 24 as au output. Thepressure signal processing module 6 may determine the pressure value 24corresponding to a given amplified signal 20 using, for example, apre-calibrated empirical relationship, or by interpolation of apre-calibrated look-up table.

The pressure signal processing module 6 does not need to be a separatemodule, and may alternatively be integrated into the device 1.

In practice, the pressure signal 19 will not be identical to thepiezoelectric response I_(piezo)(t), and may include attenuated highfrequency components of the capacitance measurement signals 21. Suchattenuated high frequency components may be compensated/removed bysubsequent digital signal processing of the amplified signal 20, forexample in the pressure signal processing module 6 or in the processor37 (FIG. 3) of an electronic device 35 (FIG. 3).

In this way, pressure and capacitance measurements may be performedusing the touch sensor 4 without the need for separate pressure andcapacitance electrodes. A single signal 18 including both pressure andcapacitance information is extracted from the touch sensor 4.Additionally, the device 1 allows the separation and amplification ofpressure and capacitance signals 19, 21 in a way which may be readilyintegrated with existing projected capacitance touch panels andcapacitive touch controllers 5.

The capacitance and pressure signal filters 15, 16 need not be high-passand low-pass filters respectively. Instead, the capacitance signalfilter 15 may he a band-pass filter having a pass-band covering thecapacitance measurement signals 21 and the pressure signal filter 16 maybe a low-pass filter with a cut-off frequency below the base frequencyf_(d). Alternatively, the capacitance signal filter 15 may be aband-pass filter having a pass-band covering the capacitance measurementsignals 21 and the pressure signal filter 16 may be a band-stop filterhaving a stop-band covering the capacitance measurement signals 21.Band-pass or band-stop filters may be notch filters when the capacitancemeasurement signals 21 have narrow frequency bandwidths, or comb filtersif the power of the capacitance measurement signals 21 is predominantlyat the base frequency f_(d) and harmonics thereof. The filters 15, 16may be passive or active, for example, the capacitance signal filter 15may simply be a capacitance, or the pressure signal filter 16 may beprovided by a resistance capacitance feedback network of an operationalamplifier providing the amplifier 17. Alternatively, more complexpassive filters may be used, for example Butterworth filters, Chebyshevfilters, Gaussian filters or Bessel filters.

The layer structure 7 of the touch sensor 4 may include only the layerof piezoelectric material 12, such that the first and second oppositefaces 8, 9 are faces of the piezoelectric material layer 12.Alternatively, the layer structure 7 may include one or more dielectriclayers which are stacked between the layer of piezoelectric material 12and the first face 8 of the layer structure 7. The layer structure 7 mayinclude one or more dielectric layers stacked between the second face 9of the layer structure 7 and the layer of piezoelectric material 12.Preferably, one or more dielectric layer(s) include layers of a polymerdielectric material such as polyethylene terephthalate (PET), or layersof pressure sensitive adhesive (PSA) material. However, one or moredielectric layer(s) may include layers of a ceramic insulating materialsuch as aluminium oxide.

In FIG. 1, the first and second faces 8, 9 and the layers of the layerstructure 7 are shown extending along orthogonal axes labelled x and y,and the thickness direction of each layer of the layer structure 7 isaligned with an axis labelled z which is orthogonal to the x and y axes.However, the first, second and thickness directions x, y, z need notform a right handed orthogonal set as shown. For example, the first andsecond directions x, y may intersect at an angle of 30 degrees or 45degrees or any other angle greater than 0 degrees and less than 90degrees.

The device 1 may be adapted to work with touch panels 36 (FIG. 5) whichinclude multiple touch sensor 4 elements, for example, by providing asignal separation stage 2 and first and second input/output terminals13, 14 corresponding to the sensing electrode 10 of each touch sensor 4included in the touch panel (FIG. 5). When adapted for multiple touchsensors 4, the device 1 includes a signal separation stage 2 for eachtouch sensor 4 (i.e. for each sensing electrode 10) so that thecapacitive touch controller 5 may measure the capacitance of eachsensing electrode 10 separately. The device may include a separateamplification stage 3 corresponding to each signal separation stage 2.

Alternatively, the number of amplification stages 3 may be less than thenumber of signal separation stages 2. For example, for a touch panel inwhich the resolution of pressure values 24 is not required to be equalto the resolution of capacitance values 23, each amplification stage 3may be connected to two or more signal separation stages 2 (FIG. 20).Although two or more signal separation stages 2 may simply be connectedto an amplification stage 3 in parallel, multiple signal separationstages 2 are preferably connected to a single amplification stage 3through a resistance network 27 (FIGS. 2, 5, 22) to minimise cross talkbetween the capacitance measurement signals 21 driving the correspondingtwo or more sensing electrodes 10.

Combined Self-Capacitance, Mutual Capacitance and Pressure Measurements

FIG. 2 illustrates a second device 25 and a second touch sensor 26 forcombined capacitance and pressure measurements. Referring also to FIG.2, a second device 25 for combined pressure and capacitance measurementsis the same as the device 1, except that the second device includes twosignal separation stages 2, two first input/output terminals 13 and twosecond input/output terminals 14 and a resistance network 27. A singleamplification stage 3 is connected to both signal separation circuits 2through the resistance network 27.

The second touch sensor 26 is similar to the first touch sensor 4,except that the second touch sensor 26 also includes a second layerstructure 28 having a third face 29 and a fourth, opposite, face 30, anda second sensing electrode 31. The second layer structure 28 includesone or more dielectric layers 32. Each dielectric layer 32 is generallyplanar and extends in first and second directions x, y which areperpendicular to a thickness direction z. The one or more dielectriclayers 32 of the second layer structure 28 are arranged between thethird and fourth faces 29, 30 such that the thickness direction z ofeach dielectric layer 32 of the second layer structure 28 isperpendicular to the third and fourth faces 29, 30. The second sensingelectrode 31 is disposed on the third face 29 of the second layerstructure 28, and the fourth face 30 of the second layer structure 28contacts the first sensing electrode 10.

Preferably, the dielectric layer(s) 32 include layers of a polymerdielectric material such as PET or layers of PSA materials. However, thedielectric layer(s ) 32 may include layers of a ceramic insulatingmaterial such as aluminium oxide. Preferably, the second sensingelectrode 31 is made of indium tin oxide (ITO) or indium zinc oxide(IZO). However, the second sensing electrode 31 may be made of aconductive polymer such as polyaniline, polythiphene, polypyrrole orpoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). Thesecond sensing electrode 31 may be a metal mesh film such as aluminium,copper, silver or other metals suitable for deposition and patterning asa thin film.

The first and second sensing electrodes 10, 31 are coupled tocorresponding ports of the capacitive touch controller 5 through therespective signal separation stages 2. Provided that the first sensingelectrode 10 does not completely screen electromagnetic interactionsbetween the piezoelectric material layer 12 and the second sensingelectrode 31, a piezoelectric response may be produced between thecommon electrode 11 and the second sensing electrode 31.

In this way, the capacitive touch controller 5 may separately measurethe self-capacitance of the first and second sensing electrodes 10, 31and at the same time measure pressure values 24 from the second touchsensor 26. Additionally, the capacitive touch controller 5 can alsomeasure the mutual capacitance between the first and second sensingelectrodes 10, 31 by, for example, driving the first sensing electrode10 using a capacitance measurement signal 21 in the form of acapacitance drive signal 33 and receiving a corresponding capacitancemeasurement signal 21 in the form of a capacitance sense signal 34induced in the second sensing electrode 31, or vice versa. Thecapacitance signal filters 15 of each signal separation stages 2 areadapted to pass the capacitance measurement signals 21 in the form ofthe capacitance drive/sense signals 33, 34. Measurement of the mutualcapacitance between the first and second sensing electrodes 10, 31 maybe more robust against electromagnetic interference compared toself-capacitance measurement. For mutual capacitance measurements, thebias signal 22 may be a fixed DC voltage or ground (0 V).

The first and second sensing electrodes 10, 31 need not share a singleamplification stage 3, and the respective signal separation stages 2 mayeach be connected to a corresponding amplification stage 3 in the sameway as the first device 1.

The second device 25 may be readily adapted for use with a touch panelincluding multiple second touch sensors 26. Instead of using coextensivefirst and second sensing electrodes 10, 31, in a touch panel 36 (FIG. 5)the first sensing electrodes 10 may be extensive in a first direction xand the second sensing electrodes 31 may be extensive in a seconddirection y, so as to form a grid in which each intersection provides asecond touch sensor 26. In such a configuration, the separation stages 2corresponding to two or more first sensing electrodes 10 may beconnected to a single amplification stage 3, or the separation stages 2corresponding to two or more second sensing electrodes 31 may beconnected to a single amplification stage 3. However, in general theseparation stages 2 corresponding to a mixture of first and secondsensing electrodes 10, 31 should not be connected to the sameamplification stage 3, except in the case that every first and secondsensing electrode 10, 31 is connected to a single amplification stage 3to provide a single, global pressure value 24 for the touch panel 36(FIG. 5).

The second layer structure 28 may include a single dielectric layer 32,such that the third and fourth opposite faces 29, 30 are faces of asingle dielectric layer 32. Alternatively, a second layer structure 28need not be used, and the second sensing electrode 31 could be disposedon the first face 8 along with the first sensing electrode 10 (FIG. 7).In FIG. 2, the third and fourth faces 29, 30 and the dielectric layers32 of the second layer structure 28 are shown extending along orthogonalaxes labelled x and y, and the thickness direction of each dielectriclayer 32 of the second layer structure 28 is aligned with an axislabelled z which is orthogonal to the x and y axes. However, the first,second and thickness directions x, y, z need not form a right handedorthogonal set as shown. The pressure signal processing module 6 doesnot need to be a separate module, and may instead be integrated into thedevice 25.

Electronic Device

FIG. 3 shows a schematic block diagram of an electronic deviceincorporating a device 1, 25 for combined pressure and capacitancemeasurements and a touch panel 36 including one or more touch sensors 4,26. Referring also to FIG. 3, an electronic device 35 may include atouch panel 36, a capacitive touch controller 5, a pressure signalprocessing module 6 and a device 1, 25 for combined capacitive andpressure measurements.

The electronic device 35 may be a relatively immobile electronic devicesuch as, for example a desktop computer, an automated teller machine(ATM), a vending machine, a point of sale device, or a public accessinformation terminal. Alternatively, an electronic device 35 may be aportable electronic device such as a laptop, notebook or tabletcomputer, a mobile phone, a smart phone, a personal data assistant, amusic playing device, or a vehicle such as a car. The preceding listsare not exhaustive. The electronic device 35 includes a touch panel 36including one or more touch sensors 4, 26. The touch panel 36 is coupledto a device for combined pressure and capacitance measurements such as,for example, the first or second device 1, 25.

The electronic device 35 may include a processor 37 for executingprograms and processing information. The electronic device 35 mayinclude a memory 38 such as a volatile random access memory fortemporarily storing programs and information, and/or storage 39 such asnon-volatile random access memory (NVRAM) or a hard disc drive (HDD) forlong term storage of programs and information. The electronic device 35may include a network interface 40 for transmitting and/or receivinginformation from wired or wireless communication networks (not shown).The electronic device 35 may include a removable storage interface 41which can interface with removable storage media (not shown) to readand/or write programs and information. The electronic device 35 mayinclude output means such as, for example, a display 42 and/orspeaker(s) 43. The display 42 may be any type of display such as, forexample, a liquid crystal display (LCD), a light emitting diode display(LED), an organic LED display, an electrophoretic display or other typeof electronic-ink display.

The capacitive touch controller 5 provides input information to theelectronic device 35 which corresponds to user interactions with thetouch panel 36. For example, input information may be the locations ofone or more user interactions. Alternatively, the capacitive touchcontroller 5 may provide capacitance values 23 to the processor 37 andthe processor 37 may determine locations of one or more userinteractions with the touch panel. Similarly, the pressure signalprocessing module 6 provides input information to the electronic device35 in the form of pressure values 24. When multiple amplification stages3 are included in the device 1, 25, the pressure signal processingmodule 6 may also provide locations of user interactions. The pressuresignal processing module 6 need not be a separate module, and mayinstead be integrated into the device 1, 25. Alternatively, the device1, 25 may provide amplified signals 20 directly to the processor 37 andthe processor 37 may determine the pressure values 24.

The electronic device may include other input means such as a microphone44, and/or other input devices 45 such as, for example, a keyboard,keypad, mouse or trackball. When the touch panel 36 includes a pluralityof touch sensors 4, 26, the capacitive touch controller 5 and/or thepressure signal processing module 6 may provide positional informationin the form of coordinates and/or pressures corresponding to one or moresimultaneous user interactions with the touch panel 36.

The touch panel 36 may be provided overlying the display 42.Alternatively, the touch sensors 4, 26 of the touch panel 36 may beintegrated into or embedded within the display 42. When the touch panel36 is used overlying or integrated into the display 42, the layerstructure(s) 7, 28 and electrodes 10, 11, 31 may be transparent orsubstantially transparent. For example, the layer structure(s) 7, 28 andelectrodes 10, 11, 31 may transmit 50% or more, preferably at least 75%,or preferably at least 90% of light in visible wavelengths. For example,the piezoelectric material may be a suitable fluoropolymer such as PVDF,dielectric layers included in the layers structures 7, 28 may be PET oran optically clear PSA, and the electrodes 10, 11, 31 may be ITO.Alternatively, the electrodes 10, 11, 31, and any connections thereto,may be opaque and sufficiently thin in a direction perpendicular to thethickness direction z that they are not immediately noticeable to thehuman eye, for example, electrodes 10, 11, 31, and any connectionsthereto, may be less than 100 micrometers (1×10-4 m) wide, less than 10micrometers (1×10-5 m) wide, or thinner.

First Touch Panel System

FIG. 4 shows a simplified cross-section of a first touch panel 36.Referring to FIGS. 1, 2 and 4, the first touch panel 36 includes layerstructures 7, 28 which are generally the same as the layer structures 7,28 of the second touch sensor 26, except that in the first touch panel36, the layer structure 7 is shared by multiple first sensing electrodes10 disposed on the first face 8 of the layer structure 7, and the secondlayer structure 28 is shared by multiple second sensing electrodes 31disposed on the third face 29 of the second layer structure 28. Thefirst sensing electrodes 10 each extend in the first direction x and thefirst sensing electrodes 10 are disposed in an array evenly spaced inthe second direction y. The second sensing electrodes 31 each extend inthe second direction y and the second sensing electrodes 31 are disposedin an array evenly spaced in the first direction x. The common electrode11 is disposed on the second face 9 and is extensive such that thecommon electrode 11 at least partially underlies each of the first andsecond sensing electrodes 10, 31. The common electrode 11 may besubstantially coextensive with the second face 9 of the layer structure7. In this way, each intersection of a first sensing electrode 10 with asecond sensing electrode 31 effectively provides a second touch sensor26. The first touch panel 36 may be bonded overlying the display 42(FIG. 3) of an electronic device 35 (FIG. 3), and a cover lens 46 (FIG.24) may be bonded overlying the first touch panel 36 to protect theoutermost electrodes, e.g. the second sensing electrodes 31.

FIG. 5 illustrates a first touch panel system 47 for combinedcapacitance and pressure measurements. Referring also to FIG. 5, thefirst touch panel system 47 includes the first touch panel 36, a thirddevice 48 for combined capacitance and pressure measurements, acapacitive touch controller 5 and a pressure signal processing module 6.

The third device 48 is the same as the first and second devices 1, 25,except that the third device 48 includes a signal separation stage 2 andfirst and second input/'output terminals 13, 14 corresponding to eachsensing electrode 10, 31. The third device 48 includes a signalseparation section 49 including a number, N, of signal separation stages2, where N is the total number of first and second sensing electrodes10, 31. The third device 48 includes N first input/output terminals 13,and each first input/output terminal 13 is connected to a correspondingfirst or second sensing electrode 10, 31 via a conductive trace 50. Thethird device 48 includes N second input/output terminals 14, and eachsecond input/output terminal is connected to a correspondingterminal/port of the capacitive touch controller. In this way, eachseparation stage 2 connects one sensing electrode 10, 31 to acorresponding terminal of the capacitive touch controller 5 through acapacitance signal filter 15 (FIG. 1).

The third device 48 includes an amplification section 51 including asecond number M of amplification stages 3. The number M of amplificationstages 3 is between one and the number N of sensing electrodes 10, 31and signal separation stages 2, i.e. 1≦M≦N. The amplification stages 3are connected to the separation stages 2 through a resistance network27. The resistance network 27 maps the M amplification stages 3 to the Nsignal separation stages such that an input of each amplification stage3 is connected to one or more sensing electrodes 10, 31 through therespective signal separation stage(s) 2.

The number M of amplification stages 3 may be equal to the number ofsensing electrodes 10, 31, so that each amplification stage 3 isconnected to one corresponding signal separation stage 2. When thenumber M of amplification stages 3 is less than the number N of sensingelectrodes 10, 31, the numbers M, N are preferably related by an integermultiple, for example, N=2×M, N=3×M, N=4×M, and each of theamplification stages 3 is preferably connected to the same number ofsignal separation stages 2 as each other amplification stage 3.Amplification stages 3 are preferably connected, through the resistancenetwork 27 and respective signal separation stage 2, to sensingelectrodes 10, 31 of the same type, for example to one or more firstsensing electrodes 10, or to one or more second sensing electrodes 31.An exception is when the amplification section 51 includes a singleamplification stage 3. In this case, the resistance network 27 connectsthe amplification stage 3 input to all of the N signal separation stages2, to allow measurement of a single, global, pressure value from thetouch panel 36.

Each amplification stage 3 outputs a corresponding amplified signal 20to the pressure signal processing module 6, which determines and outputspressure values 24 to the processor 37 (FIG. 3) of the electronic device35 (FIG. 3). Alternatively, the pressure signal processing module 6 maybe integrated into the third device 48 as a single unit.

The capacitive touch controller 5 is connected to each sensing electrode10, 31 separately. In this way, the capacitive touch controller 5 mayindividually address any sensing electrode 10, 31 or any pair includingone first sensing electrode 10 and one second sensing electrode 31. Acommon output of the capacitive touch controller 5 is connected to thecommon electrode 11 to supply bias signals 22 to the common electrode11. The connections via the signal separation stages 2 allow capacitancemeasurement signals 21, including capacitance drive/sense signals 33,34, to pass through the capacitance signal filters 15 with noattenuation or minimal attenuation. The self-capacitances of the sensingelectrodes 10, 31, or the mutual capacitances between any pair of afirst sensing electrode 10 and a second sensing electrode 31, may bemeasured by the capacitive touch controller 5 according to knownmethods, and the capacitance values 23 and/or locations of userinteractions provided to the processor 37 (FIG. 3) of the electronicdevice 35 (FIG. 3).

In this way, the first touch panel system 47 allows pressuremeasurements to be made from a touch panel, without disturbance or withminimal disturbance, to concurrent projected capacitance measurementsmade using the same set of sensing electrodes 10, 31. In this way, thenumber of sensing electrodes used is not increased compared to a purelyprojected capacitance touch panel, and there is no need to applyadditional electrodes and conducting traces 50, which could increasecross-talk and/or manufacturing complexity.

Optionally, when the amplifier 17 of the amplification stages 3 is adifferential amplifier, each signal separation stage 2 may beadditionally connected to a common terminal 52 to provide a referencepath for the differential measurement (FIGS. 10 to 13). The commonterminal 52 is connected to the common electrode 11 of the first touchpanel 36 and the common output of the capacitive touch panel 5, toreceive bias signal 22.

The device 1, 25, 48 is preferably provided as a discrete module, forexample as a packaged integrated circuit with the first and secondinput/output terminals 13, 14 and the common terminal 52 as physicalterminals for attachment to a printed circuit board or similarsubstrate. The pressure signal processing module 6 may be provided as aseparate element, or may be integrated into a single package with thedevice 48. Alternatively, the pressure signal processing module 6 may beprovided by digital signal processing in the processor 37 (FIG. 3) ofthe electronic device 35 (FIG. 3). The device 1, 25, 48 does not need tobe provided as a packaged integrated circuit, and may alternatively beprovided as a small form-factor printed circuit board which may be rigidor flexible.

An advantage of the touch panel 36 and the device 1, 25, 48 is to allowcombined capacitance and pressure measurements to be made usingconventional capacitive touch controllers 5 with minimal adaptation ofexisting hardware and software. However, the first touch panel system 47does not need to be implemented using a separate capacitive touchcontroller 5. Instead, the device 1, 25, 48, the capacitive touchcontroller 5 and the pressure signal processing module 6 may be combinedinto a single module for connection to the first touch panel 36,providing a single package solution for combined pressure andcapacitance measurements.

A separate capacitive touch controller 5 connected to the device 1, 2548 preferably has a number of capacitance measurement outputs equal tothe number N sensing electrodes 10, 31. However, capacitive touchcontrollers 5 having fewer than N capacitance measurement outputs can heused with the device 1, 25, 48 by connecting such a capacitive touchcontroller 5 to the N second input/output terminals 14 through amultiplexer. Although the first and second sensing electrodes 10, 31have been shown as being substantially rectangular, other shapes can beused.

Second Touch Panel

FIG. 6 shows a layout of first and second sensing electrodes 1, 31 for asecond touch panel 53. Referring also to FIG. 6, the second touch panel53 is the same as the first touch panel 36, except that the first andsecond sensing electrodes 10, 31 are differently shaped. Instead ofbeing rectangular, each first sensing electrode 10 may include severalpad segments 54 evenly spaced in the first direction x and connected toone another in the first direction x by relatively narrow bridgingsegments 55. Similarly each second sensing electrode 31 may includeseveral pad segments 56 evenly spaced in the second direction y andconnected to one another in the second direction y by relatively narrowbridging segments 57. The pad segments 54, 56 of the first and secondsensing electrodes 10, 31 are in the form of diamonds having a firstwidth W1, and the bridging segments 55, 57 of the first and secondsensing electrodes 10, 31 have a second width W2.

The first and second sensing electrodes 10, 31 are arranged such thatthe bridging segments 57 of the second sensing electrodes 31 overlie thebridging segments 55 of the first sensing electrodes 10. Alternatively,the first sensing electrodes 10 and the second sensing electrodes 31 maybe arranged such that the pad segments 56 of the second sensingelectrodes 31 overlie the pad segments 54 of the first sensingelectrodes 10. The pad segments 54, 56 need not be diamond shaped, andmay instead he circular. The pad segments 54, 54 may be a regularpolygon such as a triangle, square, pentagon or hexagon. The padsegments 54, 56 may be I shaped or Z shaped. The pad segments 54, 56 mayhave different areas.

Third Touch Panel

FIG. 7 shows a layout of first and second sensing electrodes 1, 31 for athird touch panel 58. Referring also FIG. 7, the third touch panel 58 issubstantially the same as the first and second touch panels 36, 53,except that the third touch panel 58 does not include the second layerstructure 28 and the second sensing electrodes 31 are disposedsubstantially on the first face 8 of the layer structure 7 along withthe first sensing electrodes 10.

Each first sensing electrode 10 is a continuous conductive regionextending in the first direction x in the same way as the second touchpanel 53. For example, each first sensing electrode 10 may includeseveral pad segments 54 evenly spaced in the first direction x andconnected to one another in the first direction x by relatively narrowbridging segments 55. Each second sensing electrode 31 may compriseseveral pad segments 59 evenly spaced in the second direction yin thesame way as the second touch panel 53. However, unlike the second touchpanel 53, the pad segments 39 of the third touch panel 58 are disposedon the first face 8 of the layer structure 7 and are interspersed with,and separated by, the first sensing electrodes 10. The pad segments 59corresponding to each second sensing electrode 31 are connected togetherby conductive jumpers 60. The jumpers 60 each span a part of a firstsensing electrode 10 and the jumpers 60 are insulated from the firstsensing electrodes 10 by a thin layer of dielectric material (not shown)which may be localised to the area around the intersection of the jumper60 and the first sensing electrode 10.

Alternatively, a thin dielectric layer (not shown) may overlie the firstface 8 of the layer structure 7, the first sensing electrodes 10 and thepad segments 59 of the second sensing electrodes 31. Conductive traces(not shown) extending in the second direction y may be disposed over thesingle thin dielectric layer (not shown), each conductive trace (notshown) overlying the pad segments 59 making up one second sensingelectrode 31. The overlying conductive traces (not shown) may connectthe pad segments 59 making up each second sensing electrode 31 usingvias (not shown) formed through the single thin dielectric layer (notshown).

Patterned Common Electrode for Touch Panels

The value of a mutual capacitance between a first or second sensingelectrode 10, 31 and the common electrode 11 may be reduced if requiredby using a patterned common electrode 11. Using a patterned commonelectrode 11 may allow the common electrode 11 to be disposed between auser's digit/stylus and the sensing electrodes 10, 31 without screeningelectrostatic interactions between the user's digit/stylus and thesensing electrodes 10, 31. A configuration with the common electrode 11towards the outside may be advantageous for touch panels integrallyembedded in a display 42 (FIGS. 32 to 39).

FIG. 8 shows a layout for a patterned common electrode 61. Referring toFIG. 8, a patterned common electrode 61 may take the form of a Cartesiangrid. The conductive region of the patterned common electrode 61includes struts 62 extending in the first direction x and having a widthW in the second direction y, and struts 63 extending in the seconddirection y and having a width W in the first direction x. The struts 61extending in the first direction x are evenly spaced in the seconddirection y with a spacing S, and the struts 63 extending in the seconddirection y are evenly spaced in the first direction x with the samespacing S. The struts 62, 63 are joined where they intersect such thatthe patterned common electrode 61 is formed of a single region ofconductive material.

Referring also to FIGS. 1, 2, 4 and 5, the patterned common electrode 61may be arranged to reduce the magnitude of the mutual capacitancesbetween the sensing electrodes 10, 31 and the common electrode 11. Apatterned common electrode 61 need not be arranged as a Cartesian grid,and any other continuously connected two-dimensional pattern may beused. A patterned common electrode 61 need not use a repeating latticepattern, and irregular or quasi-periodic arrangements may be usedinstead.

Interpolation of Pressure Values

The separation between adjacent electrodes in a projected capacitancetouch panel, sometimes referred to as the pitch, may be relativelycoarse, for example, 1 to 5 mm or larger than 5 mm. If the positions ofuser interactions were determined only at the resolution of the pitch,projected capacitance touch panels would not be able to provide accuratepositions of user interactions or smoothly follow a path traced by auser. To provide more accurate locations, projected capacitance touchpanels typically employ interpolation methods, for example, using anelectrode having a peak signal and also the adjacent electrode signals,in order to infer a touch location using linear interpolation, quadraticinterpolation or interpolation using higher order polynomials or othersuitable functions. Such interpolation is possible because a userinteraction may alter the capacitances of several adjacent sensingelectrodes simultaneously.

FIG. 9 illustrates using interpolation methods to inter a locationand/or a pressure of a user interaction. Referring to FIGS. 5 and 9,when a user presses on a cover lens 46 (FIG. 24) overlying a touch panel36, 53, 58, the layer of piezoelectric material 12 underlying the coverlens 46 will experience strain across a relatively broadened area. Forexample, this could be because the rigidity of the cover lens 46 spreadsa compressive load over a larger area and/or because the layer ofpiezoelectric material experiences in-plane stretching. For example, auser interaction at a precise location 64 applying a peak pressure 65may result in pressure values 66 a and 66 b being determined for sensingelectrodes 10, 31 at locations 67 a, 67 b which bracket the preciselocation 64. A user interaction at a precise location 64 may also resultin pressure values 68 a and 68 b being determined for sensing electrodes10, 31 at locations 69 a, 69 b which are further from the preciselocation 64 and adjacent to the pair of bracketing locations 67 a, 67 b.

The pressure values 66 a, 66 b are slightly different from the peakpressure 65 which would be measured at the precise location 64 of theuser interaction, and will vary depending on the relative position ofthe precise location 64 with respect to the bracketing locations 67 a,67 b. As such, threshold pressure values for responding to userinteractions should be spaced widely enough to avoid mis-registrationsdue to the relative position of the precise location 64 with respect tothe bracketing locations 67 a, 67 b. This may lead to a coarseresolution of pressure values for pressure touch applications. Thepotential resolution of pressure touch applications may be improved byusing interpolation to estimate the peak pressure 65.

The pressure signal processing module 6, or the processor 37 (FIG. 3)may calculate an estimate of the precise location 64 and/or the pressurevalue 65 using the largest value 66 a and the corresponding location 67a in combination with the two next nearest values 66 b, 68 a and thecorresponding locations 67 b, 69 a. Alternatively, the pressure signalprocessing module 6 or the processor 37 (FIG. 3) may calculate anestimate of the precise location 64 and/or the peak pressure 65 usingthe pair of bracketing values 66 a, 66 b and locations 67 a, 67 b. Thepressure signal processing module 6 or the processor 37 (FIG. 3) maycalculate an estimate of the precise location 64 and/or the peakpressure 65 using the pair of bracketing values 66 a, 66 b and locations67 a, 67 b and the adjacent values and locations 68 a, 68 b, 69 a, 69 b.The pressure signal processing module 6 or the processor 37 (FIG. 3) maycalculate an estimate of the precise location 64 and/or the peakpressure 65 using linear interpolation, quadratic interpolation orinterpolation using higher order polynomials or other suitablefunctions.

In this way the resolution for pressure touch applications may beimproved by applying interpolation methods to the pressure values 24 toestimate a peak pressure 65 of a user interaction. Interpolation mayalso be used to improve estimates of user interaction locationsdetermined using pressure values 24. The capacitive touch controller 5may also use interpolation of capacitance values 23 to improve theaccuracy of determining the locations of one or more user interactions.

Example Using Differential Amplification Stages

FIG. 10 illustrates an example from the third device 48 employingdifferential amplification. Referring to FIGS. 1, 2, 4, 5 and 10, in oneexample implementation, the third device 48 may include an equal numberN of differential separation stages 70 and differential amplificationstages 71. Each differential amplification stage 71 is an example ofimplementing the amplification stage 3, and each differentialamplification stage 71 includes a pressure signal filter 16 and anamplifier 17 in the form of a differential amplifier.

Each differential separation stage 70 is an example of implementing theseparation stage 2. The n^(th) differential separation stage 70 connectsthe n^(th) first input/output terminal 13 to the n^(th) secondinput/output terminal 14 through a first capacitance signal filter 15(FIG. 1). The n^(th) first input/output terminal 13 is connected to then^(th) sensing electrode 10, 31 of a touch panel 36, 53, 58 at a circuitnode denoted D. The n^(th) second input/output terminal 14 is connectedto the capacitive touch controller 5 at a circuit node denoted A. Thecapacitive touch controller 5 exchanges capacitance measurement signals21 with the n^(th) sensing electrode 10, 31 through the n^(th) secondinput/output terminal 14, for example capacitance drive/sense signals33, 34. However, the differential separation stage 70 also connects thecommon terminal 52 to the n^(th) second input/output terminal 14 througha second capacitance signal filter 15 and a referenceresistance-capacitance R_(is)-C_(is) (FIG. 11). The second capacitancesignal filter 15 and the reference resistance-capacitance (FIG. 11) areconnected in series at a circuit node denoted C. The common terminal 52is connected to the common electrode 11 of the touch panel 36, 53, 58and to the common output of the capacitive touch controller 5 at acircuit node denoted B. The common output of the capacitive touchcontroller 5 provides bias signals 22 to the common electrode 11 andcommon terminal 52.

A first input 72 to the differential amplification stage 71 is coupledto the circuit node D by a first resistance R_(d1) and a second input 73to the differential amplification stage 71 is coupled to the circuitnode C by a second resistance R_(c1). The first and second resistancesR_(d1), R_(c1) form a portion of the resistance network 27. Thedifferential amplification stage 71 produces the amplified signal 20based on the difference between the first and second inputs 72, 73, i.e.based on the voltage difference between the circuit nodes C and D.

FIG. 11 illustrates an example of a circuit of implementing thedifferential separation stage 70. Referring also to FIG. 11, the firstand second capacitance filters 15 may take the form of first and secondcapacitances, C_(i1), C_(i2). The filter capacitances C_(i1), C_(i2) mayserve as capacitance signal filters 15, namely high-pass filters, bydecoupling the capacitive touch controller from DC and low frequencycomponents. The capacitances are preferably the same. The differentialseparation stage 70 includes a reference resistance R_(is) and areference capacitance connected in series between the circuit node C andthe common terminal 52. In this way, the reference resistance R_(is) andreference capacitance provide a reference path between the capacitivetouch controller 5 and the common electrode 11.

The path between the n^(th) sensing electrode 10, 31 and the commonelectrode 11 may be approximately represented by an equivalent circuit74 for the n^(th) touch sensor 4, 26 of the touch panel 36, 53, 58. Theequivalent circuit 74 includes a sensor resistance R_(sensor)representing the resistance of the touch sensor 4, 26. The equivalentcircuit 74 includes a sensor capacitance C_(sensor), which is a mutualcapacitance between the n^(th) sensing electrode 10, 31 and the commonelectrode 11, and a piezoelectric element P_(sensor) representing thepiezoelectric material layer 12. The sensor capacitance C_(sensor) andthe piezoelectric element P_(sensor) are connected in a parallel withone another, and are connected in series with the sensor resistanceR_(sensor) at a circuit node denoted E. The equivalent circuit 74 alsoincludes a self-capacitance C_(self) of the sensing electrode 10, 31 anda variable self-capacitance ΔC_(self) which changes in response to auser interaction with the n^(th) touch sensor 4, 26. Theself-capacitance C_(self) and variable self-capacitance ΔC_(self) areconnected in parallel between the circuit node E and ground.

The value of the reference resistance R_(is) is chosen to approximatethe sensor resistance R_(sensor). The value of the reference capacitanceis chosen to approximate the overall capacitance of the network formedby the sensor capacitance C_(sensor), the piezoelectric elementP_(sensor) and the self-capacitance C_(self). In this way, the first andsecond inputs 72, 73 to the n^(th) differential amplifier 71 aresensitive to a difference between the reference path formed by thereference resistance and capacitance R_(is), C_(is), and the n^(th)touch sensor 4, 26, in response to capacitance measurement signals 21from the capacitive touch controller 5.

FIG. 12 illustrates an example of a circuit implementing thedifferential amplification stage 71. Referring also to FIG. 12, anexample of the differential amplification stage 71 includes first andsecond operational amplifiers OP1, OP2 and a comparator CM1. The firstinput 72 is received by the inverting input of the first operationalamplifier OP1 at a circuit node denoted F, and the second input 73 isreceived by the inverting input of the second operational amplifier at acircuit node denoted G. The non-inverting input of the first operationalamplifier OP1 is connected to ground through a first pull downresistance R_(x1). Similarly, the non-inverting input of the secondoperational amplifier OP2 is connected to ground through a second pulldown resistance R_(x2). The first and second pull down resistancesR_(x1), R_(x2) preferably have the same value. Optionally, first andsecond pull down capacitances C_(x1), C_(x2) may be connected inparallel with the first and second pull down resistances R_(x1), R_(x2)respectively. The output of the first operational amplifier OP1 iscoupled to the non-inverting input of the comparator CM1 at a circuitnode denoted H, and the output of the second operational amplifier OP2is coupled to the inverting input of the comparator CM1 at a circuitnode denoted I. Alternatively, the connections of the operationalamplifiers OP1, OP2 to the inverting and non-inverting inputs of thecomparator CM1 may be reversed. The comparator CM1 output provides theamplified signal 20. A first feedback resistance R_(f1) and a firstfeedback capacitance C_(f1) are connected in parallel between thecircuit node F and the circuit node H. The first feedback resistance andcapacitance R_(f1), C_(f1) provide a feedback network for the firstoperational amplifier OP1. In this way, the pressure signal filter 16 isintegrated with the first operational amplifier OP1. Similarly, a secondfeedback resistance R_(f2) and a second feedback capacitance C_(f1) areconnected in parallel between the circuit node G and the circuit node I.The second feedback resistance and capacitance R_(f1), C_(f1) providethe feedback network and pressure signal filter 16 of the secondoperational amplifier OP2. Use of differential amplification stage 71may reduce the sensitivity of the amplifier signal 20 to electromagneticinterference. The differential amplification stage 71 may also reduceany residual amplitude of the capacitance measurement signals 21.

Operation for Combined Self-Capacitance and Pressure Measurements

FIGS. 13A to 13F illustrate using the touch panel system 47 to measurethe self-capacitance of the n^(th) sensing electrode 10, 31 in a casewhen no user interaction with the n^(th) sensing electrode 10, 31 isoccurring. Referring to FIGS. 10 to 13F, the capacitive touch controller5 outputs a capacitance measurement signal 21 to the n^(th) sensingelectrode 10, 31 through the n^(th) differential separation stage 70.The capacitance measurement signal 21 may take the form of a steppedwaveform V_(self)(t), in which the voltage V_(self)(t) is held at groundfor a predetermined duration, before stepping up to a first voltage V₁.The voltage V_(self)(t) is held at V₁ for the predetermined durationbefore stepping up to a second voltage V₂ for the predetermined durationand then stepping down to a third voltage V₃. After bolding at the thirdvoltage V₃ for the predetermined duration, the voltage V_(self)(t) stepsdown to ground, i.e. 0 V, and the stepped waveform V_(self)(t) repeats.The difference between the second and third voltages, V₂-V₃ is equal tothe first voltage V₁, which allows the self-capacitance of the sensingelectrode, C_(self)+ΔC_(self) to be measured from a rising edge and afalling edge. The specific form of the voltage signal V_(self)(t) neednot be a stepped waveform, and any signal suitable for determining theself-capacitance of the n^(th) sensing electrode, C_(self)+ΔC_(self) mayhe used, depending on the capacitive touch controller 5 used.

The capacitive touch controller 5 output a bias signal 22, V_(bias)(t)which is substantially the same as the capacitance measurement signal21, V_(self)(t). This removes or substantially reduces the influence ofthe sensor capacitance C_(sensor) on the measurement of theself-capacitance C_(self)+ΔC_(self). In this way, a measured capacitancesubstantially corresponds to the self-capacitance C_(self) between then^(th) sensing electrode 10, 31 and ground. The self-capacitanceC_(self) of the n^(th) sensing electrode 10, 31 is determined by thecapacitive touch controller 5 using an internal charge amplifier (notshown) which determines the charge flowing to/from the self-capacitanceC_(self) in response to the capacitance measurement signal 21,V_(self)(t).

The capacitance measurement signal 21 is passed by the first and secondcapacitance filters 15, for example the first and second capacitancesC_(i1), C_(i2), with no or minimal attenuation. The reference resistanceand capacitance R_(is), C_(is) should preferably be chosen tosubstantially match the resistance R_(sensor) and capacitanceC_(sensor)+C_(self) of the touch sensor 4, 26 equivalent circuit 74.Thus, when no user interaction is occurring, the voltages at circuitnodes D and C, namely V_(D)(t) and V_(C)(t), are substantially similarbecause the paths to the common electrode 11 via the touch sensor 4, 26and via the reference resistance and capacitance R_(is), C_(is) havesubstantially similar impedance. Thus, the difference between thevoltages at nodes D and C, V_(D-C)(t) is small or negligible, with aresidual magnitude of δV. The residual difference V_(D-C)(t) has asubstantially similar frequency composition to the capacitancemeasurement signal 21, V_(self)(t), and is rejected/filtered out by thepressure signal filter 16 incorporated in the differential amplificationstage 72, for example the operational amplifiers OP1, OP2 and respectivefeedback networks R_(f1)-C_(f1), R_(f2)-C_(f2). The amplified signal 20,V_(amp)(t) is substantially constant. Any residual contributions due tothe capacitance measurement signal 21, V_(self)(t), which are notsufficiently attenuated by the pressure signal filter 16 and/or theintegrated nature of the output may be removed or compensated duringsubsequent digital signal processing of the amplified signal by thepressure signal processing module 6 (FIG. 5) or the processor 37 (FIG.3).

When a user interaction occurs in the form of a light press/proximityhover, i.e. no significant piezoelectric response I_(piezo)(t) isgenerated from the piezoelectric material layer 12, the signals aresubstantially the same. The change in self-capacitance ΔC_(self) of then^(th) sensing electrode 10, 31 due to the user interaction is sensed bythe capacitive touch controller 5 based on a change in the charge flowto/from the n^(th) sensing electrode which is determined by the internalcharge amplifier (not shown).

FIGS. 14A to 14I illustrate using the touch panel system 47 for combinedmeasurements of the self-capacitance of the n^(th) sensing electrode 10,31 and the pressure applied to the n^(th) sensing electrode 10, 31.Referring also to FIG. 14A to 14I, when a user interaction appliespressure to the n^(th) touch sensor 4, 26 of the touch panel 36, 53, 58,the strain induced polarisation P of the layer of piezoelectric material12 produces a piezoelectric response I_(piezo)(t) from the n^(th)sensing electrode 10, 31. The piezoelectric response I_(piezo)(t) doesnot significantly register at circuit node C via the reference pathR_(is), C_(is) because magnitude of the piezoelectric responseI_(piezo)(t) is small and because the circuit nodes C and D are at leastpartially decoupled by the first and second capacitance signal filters15, for example C_(i1) and C_(i2). In this example implementation, thepiezoelectric response I_(piezo)(t) registers at the node D as a voltageacross the input resistance R_(d1), i.e. as R_(d1)I_(piezo)(t). In thisway, the voltage signal V_(D)(t) at circuit node D is approximately asuperposition of the capacitance measurement signal 21, V_(self)(t) andthe voltage due to the piezoelectric response R_(d1)I_(piezo)(t). Thepiezoelectric signal R_(d1)I_(piezo)(t) has substantially smalleramplitude that the capacitance measurement signal 21, V_(self)(t). Therelative amplitude of the piezoelectric signal R_(d1)I_(piezo)(t) shownin FIGS. 14D to 14I has been exaggerated for visual purposes. Thedifference V_(D-C)(t) between the voltage signals at circuit nodes D andC is a superposition of the piezoelectric signal R_(d1)I_(piezo)(t) andresidual fluctuations with approximate amplitude δV. The pressure signalfilters 16 of the differential amplification stage 72 substantiallyreject/attenuate the residual fluctuations δV due to capacitancemeasurement signals 21, and the amplified signal 20, V_(amp)(t) isproportional to the integral of the piezoelectric signalR_(d1)I_(piezo)(t) multiplied by a gain G_(amp). The correspondence maynot be precise because relatively higher frequency components of thepiezoelectric signal R_(d1)I_(piezo)(t), for example above the basefrequency f_(d) of capacitance measurements signals 21, may beattenuated by the pressure signal filters 16. Any residual contributionsdue to the capacitance measurement signal 21, V_(self)(t) which are notsufficiently attenuated by the pressure signal filter 16 may be removedor compensated during subsequent digital signal processing of theamplified signal by the pressure signal processing module 6 (FIG. 5) orthe processor 37 (FIG. 3).

Referring in particular to FIGS. 14D to 14I, a user interaction applyinga pressure P_(applied) begins at t_(start) and continues until t_(end).The piezoelectric current I_(piezo)(t) (and hence to signalR_(d1)I_(piezo)(t)) increases rapidly before decaying as the chargeQ_(piezo)(t) developed between the sensing electrode 10, 31 and thecommon electrode 11 approaches a peak value. The time constant isapproximately set by the capacitance of the equivalent circuit 74 andthe input resistance R_(d1). The amplified signal 20 is proportional tothe integral of the piezoelectric signal R_(d1)I_(piezo)(t) and alsoincreases rapidly after t_(start). The amplified signal 20 also decayswith a time constant related to the amplifier. For example, the timeconstant for decay of the amplified signal 20 may be determined by theresistances R_(f1), R_(f2) and capacitances C_(f1), C_(f2) forming thefeedback network of the operational amplifiers OP1, OP2. Typically, thetime constant for decay of the amplified signal 20, V_(amp)(t) is longerthan for decay of the piezoelectric signal R_(d1)I_(piezo)(t). Once thepressure is removed at a time t_(end), a piezoelectric signal−R_(d1)I_(piezo)(t) having the opposite sense is produced as the chargeQ_(piezo) is discharged between the electrodes 10, 11, 31. The decay ofthe amplified signal 20, V_(amp)(t) results in a small, transient,overshoot of the amplified signal 20, V_(amp)(t) after t_(end). Theovershoot in the amplified signal 20, V_(amp)(t) decays to the baselinelevel with the same time constant.

In FIGS. 14D to 14I, the time constant of the piezoelectric signalR_(d1)I_(piezo)(t) has been shown as relatively short for illustrativepurposes. In practice, the time constant for decay of the piezoelectricsignal R_(d1)I_(piezo)(t) is several tens, hundreds or even thousands oftimes the period of the capacitance measurement signal 21, V_(self)(t).The duration t_(end)-t_(start) of the user interaction has also beenshortened in FIGS. 14D to 14I for illustrative purposes. In practice,the length of a user interaction may exceed hundreds, thousands or eventens of thousands of times the period of the capacitance measurementsignal 21, V_(self)(t).

The specific method for measuring the self-capacitance of the sensingelectrodes 10, 31, and the specific waveforms of the capacitancemeasurement signals 21 and bias signal 22 depend on the particularcapacitive touch controller 5 used. However, any capacitive touchcontroller 5 may be used with the device 1, 25 48, by adjusting thebandwidth of the capacitance signal filter 15 to pass the capacitancemeasurement signals 21 produced by a particular capacitive touchcontroller 5.

Operation for Combined Mutual-Capacitance and Pressure Measurements

The touch panel system 47 may also be used to measure the mutualcapacitance between a pair of one first sensing electrode 10 and onesecond sensing electrode 31, concurrently with making pressuremeasurements between each of the first and second sensing electrodes 10,31 and the common electrode. Measuring mutual capacitances between pairsof one first sensing electrode 10 and one second sensing electrode 31does not require any change in the physical configuration of the touchpanel system 47, and the measurement mode, namely self- ormutual-capacitance, mainly varies in the form of the capacitancemeasurement signals 21 sent/received by the capacitive touch controller5.

FIG. 15 illustrates using the touch panel system 47 to measure themutual capacitance between a pair of sensing electrode 10, 31. Referringto FIGS. 5, 10 to 12 and 15, mutual capacitance measurements are madeusing a pair including a first sensing electrode 10 and a second sensingelectrode 31. For example, if a touch panel 36, 53, 58 includes a totalnumber N of sensing electrodes 10, 31, of which N₁ are first sensingelectrodes, then denoting the n^(th) sensing electrode 10, 31 as E_(n),a mutual capacitance may be measured for any pairing of a first sensingelectrode 10, E_(n) for all 1≦n≦N₁ with a second sensing electrode 31,E_(k) for all N₁<k≦N.

The physical configuration of the touch panel system 47 is the same asfor self-capacitance measurements. However, the capacitive touchcontroller 5 transmits/receives different capacitance measurement.signals 21 and a mutual capacitance equivalent circuit 75 is consideredinstead of the equivalent circuit 74. The mutual capacitance equivalentcircuit 75 is substantially similar to the equivalent circuit 74. The ork^(th) touch sensor 4, 26 is represented as sensor capacitanceC_(sensor) and a sensor resistance R_(sensor) connected in seriesbetween the n^(th) sensing electrode E_(n) and the common electrode 11,with a piezoelectric element P_(sensor) connected in parallel across thesensor capacitance C_(sensor). The sensor capacitance C_(sensor)represents a mutual capacitance between the respective sensing electrodeE_(n), E_(k) and the common electrode 11. The sensor capacitanceC_(sensor) and sensor resistance R_(sensor) representing the n^(th)touch sensor 4, 26 are connected at a circuit node denoted J, and thesensor capacitance C_(sensor) and sensor resistance R_(sensor)representing the k^(th) touch sensor 4, 26 are connected at a circuitnode denoted K. The equivalent circuit 75 also includes a mutualcapacitance C_(mut)+ΔC_(mut) between the n^(th) and k^(th) sensingelectrodes E_(n), E_(k), connecting between the circuit nodes J and K.

FIGS. 16A to 16F illustrate using a touch panel system 47 to measuremutual-capacitance between an intersection of the nth sensing electrodeE_(n), 10 and the k^(th) sensing electrode E_(k), 31 when there is nouser interaction proximate to the n^(th) or k^(th) sensing electrodesE_(n), E_(k). Referring to FIGS. 4, 5, and 16A to 16F, the capacitivetouch controller 5 drives the n^(th) sensing electrode E_(n), 10 with acapacitance measurement signal 21 in the form of a capacitance drivesignal 33, V_(Tx)(t). The capacitance drive signal 33, V_(Tx)(t) takesthe form of a square wave signal have a drive signal amplitude V_(Dr)and a base frequency f_(d). The capacitive drive signal 33, V_(Tx)(t)induces a capacitance measurement signal 21 in the form of capacitancesense signal 34, V_(Rs)(t) in the intersecting k^(th) sensing electrodeE_(k), 31, and the capacitive touch controller 5 receives thecapacitance sense signal 34, V_(Rx)(t). The capacitance sense signal 34,V_(Rx)(t) is also a square wave, with an amplitude reduced to V_(D)-ΔVby a voltage drop ΔV, and the capacitive touch controller 5 determinesthe value of the mutual capacitance C_(mut) between the n^(th) andk^(th) sensing electrodes E_(n), E_(k) based on the size of the voltagedifference ΔV. The bias signal 22 is a constant DC voltage or ground formutual capacitance measurements. When there is no user interaction withthe n^(th) and k^(th) sensing electrodes E_(n), E_(k), the voltagesignals V_(C)(t), V_(D)(t) at circuit nodes C and D are substantiallysimilar, though not identical. Similar to the case of self-capacitancemeasurements, the difference signal between circuit nodes D and C,V_(D-C)(t) includes residual fluctuations δV having a frequency contentsimilar to the capacitance drive signal 33, V_(Tx)(t). The behaviour ofthe k^(th) signal separation and amplification stages 70, 71 is similar.Thus, the pressure signal filters 16 of the differential amplificationstages 71 reject/attenuate: the residual fluctuations δV and theamplified signals 20 _(n), 20 _(k), V_(amp)(t) of the n^(th) and k^(th)amplification stages 71 are substantially constant. Any remaining noisecorresponding to the capacitance drive/sense signals 33, 34 may beremoved or compensated by digital signal processing in the pressuresignal processing module 6 and/or by the processor 37 (FIG. 3).

FIGS. 17A to 17F illustrate using a touch panel system 47 to measuremutual-capacitance between an intersection of the n^(th) sensingelectrode E_(n), 10 and the k^(th) sensing electrode E_(k), 31 whenthere is a light user interaction proximate to the n^(th) or k^(th)sensing electrodes E_(n), E_(k). Referring also to FIGS. 17A to 17F, auser interaction may occur which results in capacitive coupling betweenthe user's digit or a suitable conductive stylus and the n^(th) andk^(th) sensing electrodes, but which does not apply sufficient pressureto produce a significant piezoelectric signal R_(d1)I_(piezo)(t). Thecapacitive coupling to the user's digit or conductive stylus causes achange ΔC_(mut) in the mutual capacitance between the n^(th) and k^(th)sensing electrodes. The capacitive touch controller 5 determines thechange in the mutual capacitance from a corresponding increase in thevoltage drop ΔV between the capacitance drive signal 33, V_(Tx)(t) andthe capacitance sense signal 34, V_(Rx)(t). The voltage signalsV_(C)(t), V_(D)(t) at circuit nodes C and D are also modified relativeto one another by the change in mutual capacitance ΔC_(mut), and thevoltage difference between nodes D and C, V_(D-C)(t) will changecorrespondingly. The residual voltage fluctuations δV continue to have afrequency composition based on the capacitance drive and sense signalsV_(Tx)(t), V_(Rx)(t) and are substantially rejected/attenuated by thepressure signal filters 16 incorporated in the differentialamplification stages 71.

FIGS. 18A to 18F illustrate using a touch panel system 47 to measuremutual-capacitance between an intersection of the n^(th) sensingelectrode E_(n), 10 and the k^(th) sensing electrode E_(k), 31 when auser interaction proximate to the n^(th) or k^(th) sensing electrodesE_(n), E_(k) applies sufficient pressure to induce a piezoelectricresponse. Referring also to FIGS. 18A to 18F, when a user interactionapplies pressure to the n^(th) and k^(th) touch sensors 26 of the touchpanel 36, 53, 58, the strain induced polarisation of the piezoelectricmaterial layer 12 produces a piezoelectric response I_(piezo)(t) fromthe n^(th) sensing electrode 10, 31. The piezoelectric signalI_(piezo)(t) does not substantially register at the circuit node C viathe reference path R_(is), C_(is) because the magnitude of thepiezoelectric response I_(piezo)(t) is small and because the circuitnodes C and D are at least partially decoupled by the first and secondcapacitance signal filters 15, for example C_(i1), C_(i2). In thisexample implementation, the piezoelectric response I_(piezo)(t)registers at the node D as a voltage across the input resistance R_(d1),i.e. as R_(d1)I_(piezo)(t). In this way, the voltage signal V_(D)(t) atcircuit node D is approximately a superposition of the capacitance drivesignal 33, V_(Tx)(t) and a piezoelectric signal R_(d1)I_(piezo)(t). In asimilar way, an approximate superposition of the capacitance sensesignal 34, V_(Rx)(t) and a piezoelectric signal R_(d1)I_(piezo)(t)provides one input to the differential amplification stage 71 associatedwith the k^(th) sensing electrode E_(k). The piezoelectric signalR_(d1)I_(piezo)(t) has substantially smaller amplitude than thecapacitance drive and sense signals V_(Tx)(t), V_(Rx)(t). The relativeamplitude of the piezoelectric signal R_(d1)I_(piezo)(t) shown in FIGS.18D to 18F has been exaggerated for visual purposes. The differenceV_(D-C)(t) between the voltage signals at circuit nodes D and C is asuperposition of the piezoelectric signal R_(d1)I_(piezo)(t) andresidual fluctuations δV. The pressure signal filters 16 of thedifferential amplification stage 72 substantially reject/attenuate theresidual fluctuations δV, and the amplified signal 20 _(n), V_(amp)(t)is approximately proportional to integral of the piezoelectric signal.R_(d1)I_(piezo)(t) multiplied by a gain G_(amp). As describedhereinbefore, the amplified signal V_(amp)(t) will decay towards thebaseline level for static pressures with a time constant determined bythe resistances R_(f1), R_(f2) and capacitances C_(f1), C_(f2) formingthe feedback network of the operational amplifiers OP1, OP2. Thecorrespondence may not be precise because relatively higher frequencycomponents of the piezoelectric signal R_(d1)I_(piezo)(t) (e.g. ≧f_(d))may be attenuated by the pressure signal filters 16. The amplifiedsignal 20 _(k) output by the amplification stage 71 associated with thek^(th) sensing electrode E_(k) is produced in the same way. The pressuresignal processing module 6 receives the amplified signals 20 _(n), 20_(k) and determines corresponding pressure values 24. For example, thepressure signal processing module 6 may use a model or a look-up tablepreviously calibrated using known applied pressures. A user interactionwith the n^(th) and k^(th) sensing electrodes E_(n), E_(k) results inone capacitance value 23 and a pair of pressure values 24. The pressuresignal processing module 6 may take an average of the pressure values 24calculated based on the amplified signals 20 _(n), 20 _(k) correspondingto the n^(th) and k^(th) sensing electrodes E_(n), E_(k). Alternatively,the pressure signal processing module may only determine one pressurevalue 24 based on the strongest amplified signal 20, for example, theamplified signal corresponding to the first sensing electrode 10 due toproximity to the piezoelectric material layer 12.

The first sensing electrodes 10 do not need to be the driving electrodesand the second sensing electrodes 31 do not need to be the sensingelectrodes. Instead, the capacitive touch controller 5 may drive thesecond sensing electrode 31, i.e. the k^(th) sensing electrode, usingcapacitance drive signals 33 and receive capacitance sense signals 34from the first sensing electrode 10, i.e. the n^(th) sensing electrode.

The specific method for measuring the mutual-capacitance of the sensingelectrodes 10, 31, and the specific waveforms of the capacitancemeasurement signals 21 in the form of capacitance drive/sense signals33, 34, and bias signal 22 depend on the particular capacitive touchcontroller 5 used. However, any capacitive touch controller 5 may beused with the device 1, 25, 48, by adjusting the bandwidth of thecapacitance signal filter 15 to pass the capacitance measurement signals21 produced by a particular capacitive touch controller 5.

Touch Panel System With Equal Numbers of Separation and AmplificationStages

FIG. 19 illustrates the connections between equal numbers of separationstages 2, 70 and amplification stages 3, 71. Referring to FIGS. 4, 5,10, 11 and 19, the third device 48 may be implemented using a signalseparation section 49 including a number N of separation stages 2 in theform of differential signal separation stages 70 and an amplificationsection 51 including an equal number N of amplification stages 3 in theform of differential amplification stages 71. Each differential signalseparation stage 70 is connected to one of N sensing electrodes E₁, E₂,. . . , E_(N) via a respective first input/output terminal 13. When atouch panel 36, 53, 58 includes second touch sensors 26, the sensingelectrodes E₁, E₂, . . . , E_(N) may be a mixture of first and secondsensing electrodes 10, 31, for example arranged to form a grid ofintersections.

When the numbers of differential separation and amplification stages 70,71 are equal, the resistance network 27 may include a pair ofresistances R_(en), R_(dn) corresponding to each differential separationstage 70. The resistance R_(dn) couples the first input 72 of the n^(th)differential amplification stage 71 to the circuit node D associatedwith the n^(th) differential separation stage 70. The resistance R_(en)couples the second input 73 of the n^(th) differential amplificationstage 71 to the circuit node C associated with the n^(th) differentialseparation stage 70, i.e. to the reference path R_(is)-C_(is). Thereference path R_(is)-C_(is) of each differential separation stage 70 isconnected to the common terminal 52, and the common terminal 52 isconnected to the common electrode of the touch panel 36, 53, 58.

In an alternative implementation of the touch panel system 47 usingsingle input amplification stages 77 (FIG. 21), the resistance network27 includes a single resistance coupling the input of the n^(th)amplification stage 3 to the respective n^(th) signal separation stage 2and first input/output terminal 13.

Touch Panel System With Unequal Numbers of Separation and AmplificationStages

FIG. 20 illustrates the connections between a number N of separationstages 2 in the form of differential separation stages 70 and a smallernumber M of amplification stages 3 in the form of differentialamplification stages 71. Referring to FIGS. 4, 5, 10, 11 and 20, thesignal separation section 49 may include a number N of differentialsignal separation stages 70 and the amplification section 51 may includea smaller number M of differential amplification stages 71. Eachdifferential signal separation stage 70 is connected to one of N sensingelectrodes E₁, E₂, . . . , E_(N) via a respective first input/outputterminal 13. When a touch panel includes second touch sensors 26, thesensing electrodes E₁, E₂, . . . , E_(N) may be a mixture of first andsecond sensing electrodes 10, 31, for example arranged to form a grid ofintersections.

When the number M of differential amplification stages 71 is less thanthe number N of differential separation stages 70, the resistancenetwork 27 includes a pair of resistances R_(en), R_(dn) correspondingto each differential separation stage 70. The first input 72 of them^(th) of M differential amplification stages 71 is coupled to multipledifferential separation stages 70 via the respective resistances R_(dn).For example, the m^(th) of M differential amplification stages 71 may beconnected to the n^(th) and n+1^(th) differential separation stages 70via the respective resistances R_(dn), R_(dn+1). In this case, the firstinput/output terminal of each resistance R_(dn), R_(dn+1) is connectedto the circuit node D associated with the respective differentialseparation stage 70, and the second input/output terminals of bothresistances R_(dn), R_(dn+1) are connected to the first input 72 of thecorresponding m^(th) differential amplification stage 71 at a commoncircuit node. The second input 73 of the differential amplificationstage 71 is connected to the corresponding differential separationstages 70 by the resistances R_(en), R_(en+1) in the same way.

In this way, the amplified signal 20 output by the m^(th) of Mdifferential amplification stages 71 will be indicative of a pressureapplied proximate any one of the sensing electrodes E_(n), E_(n+1) whichare connected to the m^(th) differential amplification stage 71 throughthe respective n^(th) and n+1^(th) differential separation stages 70.When the amplification stages 71 include integrating amplifiers, theamplified signal 30 will be indicative of a sum of the pressures appliedproximate to the sensing electrodes E_(n), E_(n+1) which are connectedto the m^(th) differential amplification stage 71. More than twodifferential separation stages 70 may be connected to each differentialamplification stage 71 in an analogous way.

In an alternative implementation of the touch panel system using singleinput amplification stages 77 (FIG. 21, the amplification stages 3 mayhe connected to the signal separation stages 2 in the same way, exceptthat each signal separation stage 2 will correspond to a singleresistance R_(dn) within the resistance network 27.

Touch Panel System Using Single Input Amplification Stages

FIG. 21 illustrates an example implementation of a portion of a touchpanel system 47 employing single input separation and amplificationstages 76, 77. Referring to FIGS. 1, 2, 4, 5 and 21, the first touchpanel system may be implemented using amplification stages 3 in the formof single input amplification stages 77, and corresponding signalseparation stages 2 in the form of single input signal separation stages76. A single input amplification stage 77 may generate the amplifiedsignal 20 based on a single input 78. An n^(th) single input signalseparation stage 76 may couple the n^(th) second input/output terminal14 to the n^(th) first input/output terminal 13 through a capacitanceC_(i1) providing a first capacitance signal filter 15. The n^(th) firstinput/output terminal 13 is connected to the capacitance at a circuitnode denoted D, which is also coupled to the first input 78 of thecorresponding single input amplification stage 77 via a resistanceR_(dn).

An example implementation of the single input amplification stage 77includes a first operational amplifier OP1 having an inverting inputcoupled to the first input 78 at a circuit node denoted L. Thenon-inverting input of the first operational amplifier OP1 is coupled toground via a pull down resistance R_(xn). Optionally, a pull downcapacitance C_(xn) is connected in parallel across the pull downresistance R_(xn). The output of the first operational amplifier OP1 isconnected to a circuit node denoted M which provides the amplifiedsignal 20. A feedback resistance R_(fn) and a feedback capacitanceC_(fn) are connected in parallel between the circuit nodes L and M,providing a feedback network for the first operational amplifier OP1.

Referring also to FIGS. 13 and 14, single input separation andamplification stages 76, 77 may be used for combined self-capacitanceand pressure measurements using first or second touch sensors 4, 26.

Referring also to FIGS. 16 to 18, single input separation andamplification stages 76, 77 may be used for combined mutual-capacitanceand pressure measurements using first or second touch sensors 4, 26.

Referring also to FIG. 19, single input separation and amplificationstages 76, 77 may be used in touch panel systems including equal numbersof single input separation and amplification stages 76, 77.

Referring also to FIG. 20, single input separation and amplificationstages 76, 77 may be used in touch panel systems including a firstnumber of single input separation stages 76 and a second, lower, numberM of single input amplification stages 77.

As already explained, the amplitude of capacitance measurement signals21, for example capacitance drive and sense signals 33, 34, issubstantially larger than the amplitude of piezoelectric signalR_(d1)I_(piezo)(t). Differential amplification stages 71 are preferred,because using the reference path to provide a second input means thatthe pressure signal filter 16 must attenuate the amplitude of residualvoltage fluctuations δV, which is considerably less than the fullamplitude of capacitance measurement signals 21 such as V_(self)(t) orV_(Tx)(t). By contrast, using single input amplification stages 77, thepressure signal filter 16 must attenuate the full amplitude of thecapacitance measurement signals 21. As a result, amplified signals 20output by single input amplification stages 77 may include relativelymore significant noise signals corresponding to capacitance measurementssignals 21. Any remaining noise signals corresponding to the capacitancemeasurement signals 21 may be removed or compensated by digital signalprocessing in the pressure signal processing module 6 and/or in theprocessor 37 (FIG. 3).

Second Touch Panel System

FIGS. 22 and 23 illustrate a second touch panel system 79. Referring toFIGS. 1, 22 and 23, a second touch panel system 79 includes a fourthtouch panel 80 and the third device 48. The fourth touch panel 80includes a number of first sensing electrodes 10 in the form of discretepads 81, each pad 81 connected to a corresponding first input/outputterminal 13 of the third device 48 by a separate conductive trace 50.The fourth touch panel 80 includes the layer structure 7 incorporating alayer of piezoelectric material 12. The fourth touch panel 80 does notinclude the second layer structure 38 or any second sensing electrodes31. The fourth touch panel may be used with the third device 48 forcombined self-capacitance and pressure measurements.

In the second touch panel system 79, the third device 48 may useseparation and amplification stages 2, 3 in the form of differentialseparation and amplification stages 70, 71, or single input separationand amplification stages 76, 77. In the second touch panel system 79,the third device 48 may have equal numbers of separation andamplification stages 2, 3 (FIG. 19), or the third device may have afirst number N of separation stages 2 and a second, lower, number M ofamplification stages 3.

First Display Stack Up

FIG. 24 illustrates a first stack-up 82. Referring to FIG. 24, a firststack-up 82 includes a cover lens 46 which is a transparent substrateextending in the first and second directions x, y and having upper andlower opposite faces with respect to the thickness direction z. Thefirst stack-up 82 also includes a first dielectric layer 83 extending inthe first and second directions x, y and having upper and lower oppositefaces with respect to the thickness direction z. Second sensingelectrodes 31 in the form of a set of conductive regions extending inthe first direction x and spaced apart in the second direction y aredisposed on the upper face of the first dielectric layer 83. The upperface of the first dielectric layer 83 is bonded to the lower face of thecover lens 46.

The first stack-up 82 also includes a second dielectric layer 84extending in the first and second directions x, y and having upper andlower opposite faces with respect to the thickness direction z. Firstsensing electrodes 10 in the form of a set of conductive regionsextending in the second direction y and spaced apart in the lintdirection x are disposed on the upper face of the second dielectriclayer 84. The upper face of the second dielectric layer 84 is bonded tothe lower face of the first dielectric layer 83.

The first stack-up 82 also includes a layer of piezoelectric material 12extending in the first and second directions x, y and having upper andlower opposite faces with respect to the thickness direction z. A commonelectrode 11 in the form of a conductive material region is disposed onthe lower face of the layer of piezoelectric material 12 such that, whenassembled, the common electrode 11 at least partially overlaps eachfirst and second sensing electrode 10, 31 region. The upper face of thelayer of piezoelectric material 12 is bonded to the lower face of thesecond dielectric layer 84.

The first display stack-up 82 may be bonded overlying the display 42 ofan electronic device 35 (FIG. 3). The elements of the first displaystack-up 82 are stacked in the thickness direction z from the display 42to the cover lens 46. The layer structure 7 includes the seconddielectric layer 84 and the layer of piezoelectric material 12 and thesecond layer structure 28 includes the first dielectric layer 83.

The cover lens 46 is made of glass, or PET or any other substantiallytransparent material. The cover lens 46 may be up to about 20 mm thickand may be at least 0.05 mm thick. Preferably, the cover lens 46 is upto about 2 mm thick and may be at least 0.05 mm thick. The layer ofpiezoelectric material 12 is made of PVDF or any other substantiallytransparent piezoelectric material. The layer of piezoelectric material12 may be poled before assembling the first stack-up 82. Alternatively,the layer of piezoelectric material 12 may be poled after assembling thefirst stack-up 82. The layer of piezoelectric material 12 may be up toabout 110 μm thick, and may be at least 0.5 μm or at least 1 μm thick.The common electrode 11 and the first and/or second sensing electrodes10, 31 may be used to produce a poling field. The dielectric layers 83,84 may be PET or any other substantially transparent polymer. Thedielectric layers 83, 84 may be between 10 μm and 100 μm thick, forexample, around 20 to 25 μm thick. Preferably the dielectric layers 83,84 are in the range of about 10-100 μm thick. The conductive regionsproviding the electrodes 10, 11, 31 may be ITO, IZO or any othersubstantially transparent conductive material. The conductive regionsproviding the electrodes 10, 11, 31 may be applied to the dielectriclayers 83, 84 and/or the layer of piezoelectric material 12 usinglithography, printing or other suitable methods. The shapes of theconductive regions providing the first, second and third electrodes 10,11, 31 may be any suitable electrode shape described in relation to, forexample, one of the first or second touch panels 36, 53. The sheetresistance of conductive regions providing electrodes may be between 1and 300 Ω/sq. The sheet resistance may be below 10 Ω/sq. The resistanceof an individual sensing electrode 10, 31 and connecting trace may be upto 5 kΩ or up to 10 kΩ.

The elements of the first display stack-up may he bonded together in anyother sequence resulting in the same ordering of layers 83, 84, 12. Inparticular, the first and second dielectric layers 83, 84 and the layerof piezoelectric material 12 may be bonded together using continuousroll-to-roll production methods before being bonded to the cover lens46. When the cover lens 46 is a flexible material, the first displaystack-up 82 may be fabricated entirely using continuous roll-to-rollprocesses.

The first display stack-up 82 does not require complex patterning of thelayer of piezoelectric material 12 or of electrodes 10, 11, 31 disposedon the layer of piezoelectric material 12. This allows fabrication ofthe first display stack-up to avoid complex multi-stage and/or duplexpatterning of electrodes. As a result, fabrication of the first displaystack up 82 may be fast, efficient and cheap.

Second Display Stack Up

FIG. 25 illustrates a second display stack-up 85. Referring also to FIG.25, the second display stack-up 85 is the same as the first displaystack-up 82, except that elements of the second display stack-up 85 arebonded to one another using layers of pressure sensitive adhesive (PSA)material 86 extending in the first and second directions x, y. Forexample, the cover lens 46 and the first dielectric layer 83 arearranged so that the lower face of the cover lens 46 is opposite to theupper face of the first dielectric layer 83 and separated by a layer ofPSA 86. Pressure applied in the thickness direction z bonds the coverlens 46 and the first dielectric layer 83 together. Layers of PSAmaterial 86 are used in the same way to bond the first and seconddielectric layers 83, 84, to bond the second dielectric layer 84 to thelayer of piezoelectric material 12 and to bond the second stack-up 85overlying the display 42. Layers of PSA material 86 may be between 10and 50 μm thick. Preferably, the layers of PSA material 86 are 25 μmthick.

The elements of the second display stack-up 85 are stacked in thethickness direction z from the display 42 to the cover lens 46. Thelayer structure 7 includes the second dielectric layer 84, the layer ofpiezoelectric material 12 and a layer of PSA material 86. The secondlayer structure 28 includes the first dielectric layer 83 and a layer ofPSA material 86.

Third Display Stack-Up

FIG. 26 illustrates a third display stack-up 87. Referring also to FIG.26, a third display stack up 87 includes a cover lens 46 which is atransparent substrate extending in the first and second directions x, yand having upper and lower opposite fares with respect to the thicknessdirection z. A first dielectric layer 83 extends in the first and seconddirections x, y and has upper and lower opposite faces with respect tothe thickness direction z. Second sensing electrodes 31 in the form of aset of conductive regions extending in the first direction x and spacedapart in the second direction y are disposed on the upper face of thefirst dielectric layer 83. The upper face of the first dielectric layer83 is bonded to the lower face of the cover lens 46 using a layer of PSAmaterial 86.

The third display stack up 87 also includes a layer of piezoelectricmaterial 12 extending in the first and second directions x, y, andhaving upper and lower opposite faces with respect to the thicknessdirection z. First sensing electrode 10 in the form of conductiveregions extending in a second direction y and spaced apart in the firstdirection x are disposed on the upper face of the layer of piezoelectricmaterial 12. A common electrode 11 in the form of a conductive materialregion is disposed on the lower face of the layer of piezoelectricmaterial 12 such that, when assembled, the common electrode 11 at leastpartially overlaps each of the first and second sensing electrodes 10,31. The upper face of the layer of piezoelectric material 12 may bebonded to the lower face of the first dielectric layer 83 using a layerof PSA material 86.

The third display stack up 87 may he bonded overlying the display 42using a layer of PSA material 86.

The elements of the third display stack-up 87 are stacked in thethickness direction z from the display 42 to the cover lens 46. Thelayer structure 7 includes the layer of piezoelectric material 12. Thesecond layer structure 28 includes the first dielectric layer 83 and alayer of PSA material 86.

Fourth Display Stack-Up

FIG. 27 illustrates a fourth display stack-up 88. Referring also to FIG.27, a fourth display stack up 88 includes a cover lens 46 which is atransparent substrate extending in the first and second directions x, yand having upper and lower opposite faces with respect to the thicknessdirection z. The fourth display stack up 88 also includes a firstdielectric layer 83 extending in the first and second directions x, yand having upper and lower opposite faces with respect to the thicknessdirection z. Second sensing electrodes 31 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the upper face of the firstdielectric layer 83. The upper face of the first dielectric layer 83 isbonded to the lower face of the cover lens 46 using a layer of PSAmaterial 86.

The fourth display stack up 88 also includes a second dielectric layer84 extending in the first and second directions x, y and having upperand lower opposite faces. First sensing electrodes 10 in the fibrin of aset of conductive regions extending in the second direction y and spacedapart in the first direction x are disposed on the upper face of thesecond dielectric layer 84. The upper face of the second dielectriclayer 84 is bonded to the lower face of the first dielectric layer 83using a layer of PSA material 86.

The fourth display stack up 88 also includes a layer of piezoelectricmaterial 12 extending in the first and second directions x, y and havingupper and lower opposite faces. The upper face of the layer ofpiezoelectric material 12 is bonded to the lower face of the seconddielectric layer 84 using a layer of PSA material 86.

The fourth display stack up 88 also includes a third dielectric layer 89extending in the first and second directions x, y and having upper andlower opposite faces with respect to the thickness direction z. A commonelectrode 11 in the form of a conductive material region is disposed onthe upper face of the third dielectric layer 89 such that, whenassembled, the common electrode 11 at least partially overlaps each ofthe first and second sensing electrodes 10, 31. The third dielectriclayer 89 is substantially the same as the first or second dielectriclayers 83, 84. The upper face of the third dielectric layer 89 is bondedto the lower face of the layer of piezoelectric material 12 using alayer of PSA material 86.

The fourth display stack-up 88 may he bonded overlying the display 42 ofan electronic device 35 (FIG. 3). The elements of the fourth displaystack up 88 are stacked in the thickness direction z from the display 42to the cover lens 46. The layer structure 7 includes the seconddielectric layer 84, the layer of piezoelectric material 12 and twolayers of PSA material 86. The second layer structure 28 includes thefirst dielectric layer 83 and a layer of piezoelectric material 86.

In this way, the layer of piezoelectric material 10 of the fourthdisplay stack-up 88 does not have any electrodes disposed thereon. Thissimplifies the fabrication of the fourth stack-up 88 because processingsteps to deposit electrodes on the layer of piezoelectric material 12are not required. In a case when the layer of piezoelectric material 12is PVDF, the fourth stack-up 88 can be fabricated by sandwiching a PVDFfilm providing the layer of piezoelectric material 12 between PET layersbearing patterned ITO electrodes, for example first and seconddielectric layers 83, 84, and unpatterned ITO electrodes, for examplethe third dielectric layer 89. In this way, methods for manufacturing aregular projected capacitance touch panel may be quickly and easilyadapted to allow production of combined pressure and capacitance touchpanels.

Fifth Display Stack-Up

FIG. 28 illustrates a fifth display stack-up 90. Referring also to FIG.28, a fifth display stack up 88 includes a cover lens 46, which is atransparent substrate extending in the first and second directions x, yand having upper and lower opposite faces with respect to the thicknessdirection z. The fifth display stack up 88 also includes a fourthdielectric layer 91 extending in the first and second directions x, yand having upper and lower opposite faces with respect to the thicknessdirection z. Second sensing electrodes 31 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the upper face of the fourthdielectric layer 91. First sensing electrodes 10 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the lower face of the fourthdielectric layer 91. The upper face of the fourth dielectric layer 91 isbonded to the lower face of the cover lens 46 using a layer of PSAmaterial 86. The fourth dielectric layer 91 is substantially the same asthe first, second or third dielectric layers 83, 84, 89.

The fifth display stack up 88 also includes a layer of piezoelectricmaterial 12 extending in the first and second directions x, y and havingupper and lower opposite faces. A common electrode 11 in the form of aconductive material region is disposed on the lower face of the layer ofpiezoelectric material 12 such that, when assembled, the commonelectrode 11 at least partially overlaps each of the first and secondsensing electrodes 10, 31. The upper face of the layer of piezoelectricmaterial 12 is bonded to the lower face of the fourth dielectric layer91 using a layer of PSA material 86.

The fifth display stack-up 90 may be bonded overlying the display 42 ofan electronic device 35 FIG. 3) using a layer of PSA material 86. Theelements of the fifth display stack-up 90 are stacked in the thicknessdirection z from the display 42 to the cover lens 46. The layerstructure 7 includes the layer of piezoelectric material 12 and a layerof PSA material 86. The second layer structure 28 includes the fourthdielectric layer 91.

The common electrode 11 need not be disposed on the layer ofpiezoelectric material 12. Alternatively, the fifth display stack-up 90may include the third dielectric layer 89 with the upper face of thethird dielectric layer 89 bonded to the lower face of the layer ofpiezoelectric material 12 using a layer of PSA material 86.

Sixth Display Stack-Up

FIG. 29 illustrates a sixth display stack-up 92. Referring also to FIG.29, a sixth display stack up 92 includes a cover lens 46 which is atransparent substrate extending in the first and second directions x, yand having upper and lower opposite faces with respect to the thicknessdirection. The sixth display stack up 92 also includes a fifthdielectric layer 93 extending in the first and second directions x, yand having upper and lower opposite fares with respect to the thicknessdirection z. Second sensing electrodes 26 in the form of a set ofconductive regions extending in the first direction x and spaced apartin the second direction y are disposed on the upper face of the fifthdielectric layer 93. First sensing electrodes 10 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the upper face of the fifthdielectric layer 93. The upper face of the fifth dielectric layer 93 isbonded to the lower face of the cover lens 46 using a layer of PSAmaterial 86. The fifth dielectric layer 93 is substantially the same asthe first, second, third or fourth dielectric layers 83, 84, 89, 91.Each first sensing electrode 10 is a continuous conductive region andeach second sensing electrode 31 is made up of a number of separateconductive regions connected by jumpers 100. Each jumper spans a portionof a conductive region belonging to a first sensing electrode 10. Thefirst and second sensing electrodes 10, 31 may be substantially the sameas the first and second sensing electrodes 10, 31 of the third touchpanel 58.

The sixth display stack up 92 also includes a layer of piezoelectricmaterial 12 extending in the first and second directions x, y and havingupper and lower opposite faces with respect to the thickness directionz. A common electrode 11 in the form of a conductive material region isdisposed on the lower face of the layer of piezoelectric material 12such that, when assembled, the common electrode 11 at least partiallyoverlaps each of the first and second sensing electrodes 10, 31. Theupper face of the layer of piezoelectric material 12 is bonded to thelower face of the fifth dielectric layer 93 using a layer of PSAmaterial 86.

The sixth display stack-up 92 may be bonded overlying the display 42 ofan electronic device 35 (FIG. 3) using a layer of PSA material 88. Theelements of the sixth display stack-up 92 are stacked in the thicknessdirection z from the display 42 to the cover lens 46. The layerstructure 7 includes the layer of piezoelectric material 12, a layer ofPSA material 86 and the fifth dielectric layer 93.

The common electrode 11 need not be disposed on the layer ofpiezoelectric material 12. Alternatively, the sixth display stack-up 92may include the third dielectric layer 89 with the upper face of thethird dielectric layer 89 bonded to the lower face of the layer ofpiezoelectric material 12 using a layer of PSA material 86.

Seventh Display Stack-Up

FIG. 30 illustrates a seventh display stack-up 94. Referring also toFIG. 30, a seventh display stack up 94 includes a cover lens 46 which isa transparent substrate extending in the first and second directions x,y and having upper and lower opposite faces with respect to thethickness direction z. Second sensing electrodes 31 in the form of a setof conductive regions extending in the first direction x and spacedapart in the second direction y are disposed on the lower face of thecover lens 46.

The seventh display stack up 94 also includes the second dielectriclayer 84 extending in the first and second directions x, y and havingupper and lower opposite faces with respect to the thickness directionz. First sensing electrodes 10 in the form of a set of conductiveregions extending in the second direction y and spaced apart in thefirst direction x are disposed on the upper face of the seconddielectric layer 84. The upper face of the second dielectric layer 84 isbonded to the lower face of the cover lens 46 using a layer of PSAmaterial 86.

The seventh display stack up 94 also includes a layer of piezoelectricmaterial 12 extending in the first and second directions x, y and havingupper and lower opposite faces with respect to the thickness directionz. A common electrode 11 in the form of a conductive material region isdisposed on the lower face of the layer of piezoelectric material 12such that, when assembled, the common electrode 11 at least partiallyoverlaps each of the first and second sensing electrodes 10, 31. Theupper face of the layer of piezoelectric material 12 is bonded to thelower face of the second dielectric layer 84 using a layer of PSAmaterial 86.

The seventh display stack-up 94 may be bonded overlying the display 42of an electronic device 35 (FIG. 3) using a layer of PSA material 86.The elements of the seventh display stack-up 94 are stacked in thethickness direction z from the display 42 to the cover lens 46. Thelayer structure 7 includes the layer of piezoelectric material 12, alayer of PSA material 86 and the second dielectric layer 84. The secondlayer structure 28 includes a layer of PSA material 86.

The common electrode 11 need not be disposed on the layer ofpiezoelectric material 12. Alternatively, the seventh display stack-up94 may include the third dielectric layer 89 with the upper face of thethird dielectric layer 89 bonded to the lower face of the layer ofpiezoelectric material 12 using a layer of PSA material 86.

Eighth Display Stack-Up

FIG. 32 illustrates an eighth display stack-up 95. Referring also toFIG. 32, an eighth display stack up 95 includes a cover lens 46 which isa transparent substrate extending in the first and second directions x,y and having upper and lower opposite faces with respect to thethickness direction z. Second sensing electrodes 31 in the form of a setof conductive regions extending in the first direction x and spacedapart in the second direction y are disposed on the lower face of thecover lens 46. First sensing electrodes 10 in the form of a set ofconductive regions extending in the second direction y and spaced apartin the first direction x are disposed on the lower face of the coverlens 46. Each first sensing electrode 10 is a continuous conductiveregion and each second sensing electrode 31 is made up of a number ofseparate conductive regions connected by jumpers 100. Each jumper spansa portion of a conductive region belonging to a first sensing electrode10. The first and second sensing electrodes 10, 31 may be substantiallythe same as the first and second sensing electrodes 10, 31 of the thirdtouch panel 58.

The eighth display stack up 95 also includes a layer of piezoelectricmaterial 12 extending in the first and second directions x, y and havingupper and lower opposite faces with respect to the thickness direction.The upper face of the layer of piezoelectric material 12 is bonded tothe lower face of the cover lens 46 using a layer of PSA material 86.

The eighth display stack up 95 also includes a third dielectric layer 89extending in the first and second directions x, y and having upper andlower opposite faces. A common electrode 11 in the form of a conductivematerial region is disposed on the upper face of the third dielectriclayer 89 such that, when assembled, the common electrode 11 at leastpartially overlaps each of the first and second sensing electrodes 10,31. The upper face of the third dielectric layer 89 is bonded to thelower face of the layer of piezoelectric material 12 using a layer ofPSA material 86.

The eighth display stack-up 95 may be bonded overlying the display 42 ofan electronic device 35 (FIG. 3) using a layer of PSA material 86. Theelements of the eighth display stack-up 95 are stacked in the thicknessdirection z from the display 42 to the cover lens 46. The layerstructure 7 includes the layer of piezoelectric material 12 and twolayers of PSA material 86.

First Embedded Stack-Up

The first to eighth display stack-ups 82, 85, 87, 88, 90, 92, 94, 95 areintended to overlie the display 42 of an electronic device 35 (FIG. 3).However, a touch panel 36, 53, 58 for use with the third device 48 forcombined capacitance and pressure measurements may alternatively beintegrated into a display 42 such as, for example, an LCD display, anOLED display, a plasma display or an electrophoretic display.

FIG. 32 shows a first embedded stack-up 96. Referring also to FIG. 32, afirst embedded stack-up 96 includes a pixel array 97 of a display 42, acolour filter glass 98, first and second sensing electrodes 10, 31, alayer structure 7, a patterned common electrode 61, a polariser 99 and acover lens 46 stacked in the thickness direction from the pixel array 97to the cover lens 46. The first and second sensing electrodes 10, 31 maybe disposed on the same surface in substantially the same way as thethird touch panel 58.

In this way, the first embedded stack-up 96 can be used with the thirddevice 48 to provide a touch panel with combined capacitive and pressuresensing embedded within an LCD display. This may allow the totalthickness of the display 42 and touch panel to be reduced compared to atouch panel overlying the display 42.

Using patterned common electrode 61 may help to prevent the commonelectrode 61 from screening the capacitive coupling between a user'sdigit and/or conductive stylus and the first and second sensingelectrodes 10, 31.

Second Embedded Stack-Up

FIG. 33 shows a second embedded stack-up 100. Referring also to FIG. 33,a second embedded stack-up 101 includes a pixel array 97 of a display42, a colour filter glass 98, first and second sensing electrodes 10,31, a polariser 99, a layer structure 7, a patterned common electrode 61and a cover lens 46 stacked in the thickness direction from the pixelarray 97 to the cover lens 46. The first and second sensing electrodes10, 31 may be disposed on the same surface in substantially the same wayas the third touch panel 58.

Third Embedded Stack-Up

FIG. 34 shows a third embedded stack-up 101. Referring also to FIG. 34,a third embedded stack-up 101 includes a pixel array 97 of a display 42,second sensing electrodes 31 a colour filter glass 98, first sensingelectrodes 10, a layer structure 7, a patterned common electrode 61, apolariser 99 and a cover lens 46 stacked in the thickness direction fromthe pixel array 97 to the cover lens 46. The first and second sensingelectrodes 10, 31 are disposed on opposite sides of the colour filterglass 98 instead of being separated by a second layer structure 28.

Fourth Embedded Stack-Up

FIG. 35 shows a fourth embedded stack-up 102. Referring also to FIG. 35,a fourth embedded stack-up 102 includes a pixel array 97 of a display42, second sensing electrodes 31, a colour filter glass 98, firstsensing electrodes 10, a polariser 99, a layer structure 7, a patternedcommon electrode 61 and a cover lens 46 stacked in the thicknessdirection from the pixel array 120 to the cover lens 77. The first andsecond sensing electrodes 10, 31 are disposed on opposite sides of thecolour filter glass 98 instead of being separated by a second layerstructure 28.

Fifth Embedded Stack-Up

FIG. 36 shows a fifth embedded stack-up 103. Referring also to FIG. 36,a fifth embedded stack-up 103 includes a pixel array 97 of a display 42,second sensing electrodes 31, a second layer structure 28, first sensingelectrodes 10, a colour filter glass 98, a layer structure 7, apatterned common electrode 61, a polariser 99 and a cover lens 46stacked in the thickness direction from the pixel array 97 to the coverlens 46. The first and second sensing electrodes 10, 31 are separated bythe second dielectric layer 28.

Sixth Embedded Stack-Up

FIG. 37 shows a sixth embedded stack-up 104. Referring also to FIG. 37,a sixth embedded stack-up 104 includes a pixel array 97 of a display 42,second sensing electrodes 31, a second layer structure 28, first sensingelectrodes 10, a layer structure 7, a colour filter glass 98, apatterned common electrode 61, a polariser 99 and a cover lens 46stacked in the thickness direction from the pixel array 97 to the coverlens 46. The first and second sensing electrode 10, 31 are separated bythe second dielectric layer 28.

Seventh Embedded Stack-Up

FIG. 38 shows a seventh embedded stack-up 105. Referring also to FIG.38, a seventh embedded stack-up 105 includes a pixel array 97 of adisplay 42, second sensing electrodes 31, a second layer structure 28,first sensing electrodes 10, a layer structure 7, a patterned commonelectrode 61, a colour filter glass 98, a polariser 99 and a cover lens46 stacked in the thickness direction from the pixel array 97 to thecover lens 46. The first and second sensing electrode 10, 31 areseparated by the second dielectric layer 28.

Eighth Embedded Stack-Up

FIG. 39 shows an eighth embedded stack-up 106. Referring also to FIG.39, an eighth embedded stack-up 106 includes a pixel array 97 of adisplay 42, second sensing electrodes 31, a second layer structure 28,first sensing electrodes 10, a colour filter glass 98, a polariser 99, alayer structure 7, a patterned common electrode 61 and a cover lens 46stacked in the thickness direction from the pixel array 97 to the coverlens 46. The first and second sensing electrode 10, 31 are separated bythe second dielectric layer 28.

In the first to eighth embedded stack-ups 96, 100, 101, 102, 103, 104,105, 106 the first and second sensing electrodes 10, 31 and thepatterned common electrode 61 may be disposed on the surfaces ofadjacent elements disposed above or below with respect to the thicknessdirection z. Alternatively, the first and second sensing electrodes 10,31 and the patterned common electrode 61 may be disposed on the surfacesof additional dielectric layers similar to the first, second, third,fourth and fifth dielectric layers 83, 84, 89, 91, 93. A patternedcommon electrode 61 need not be used and an unpatterned common electrode11 may be used instead provided that capacitive coupling between auser's digit and/or conductive stylus and the first and/or secondsensing electrodes 10, 31 is not excessively screened. Additional PSAlayers 86 may be used to bond one or more layers of the first to eighthembedded stack-ups 96, 100, 101, 102, 103, 104, 105, 106.

Modifications

It will be appreciated that many modifications may be made to theembodiments hereinbefore described. Such modifications may involveequivalent and other features which are already known in the design,manufacture and use of capacitive touch panels and which may he usedinstead of or in addition to features already described herein. Featuresof one embodiment may be replaced or supplemented by features of anotherembodiment. For example, features of one display stack-up or embeddeddisplay stack-up may be replaced or supplemented by features of otherdisplay stack-ups and/or other embedded display stack-ups.

Touch panels have been described in which first and second sensingelectrodes 10, 31 are separated from a common electrode 11, 61 by thelayer structure 7. However, other arrangements are possible. Referringto FIGS. 40 and 41, a fifth touch panel 107 includes a layer structure7, a plurality of first sensing electrodes 10 disposed on the first face8 of the layer structure 7, a plurality of second sensing electrodes 31disposed on the second thee 9 of the layer structure 7 and a pluralityof common electrodes 11 disposed on the second face 9 of the layerstructure 7 in the form of a plurality of separated common electrodes108.

The first sensing electrodes 10 extend in the first direction x and arespaced apart in the second direction y. The second sensing electrodes 31extend in the second direction y and are spaced apart in the firstdirection x. The separated common electrodes 108 extend in the seconddirection y and are spaced apart in the first direction x. The separatedcommon electrodes 108 and the second sensing electrodes 31 areinterleaved and do not contact one another. The separated commonelectrodes 108 and second sensing electrodes 31 may be read usingconductive traces (not shown) which exit the fifth touch panel 107 ondifferent edges. Each first sensing electrode 10 may take the form ofseveral pad segments 54 evenly spaced in the first direction x andconnected to one another in the first direction x by relatively narrowbridging segments 55. Similarly, each second sensing electrode 31 mayinclude several pad segments 56 evenly spaced in the second direction yand connected to one another in the second direction y by relativelynarrow bridging segments 57. The pad segments 54 of the first sensingelectrodes 10 may be diamond shaped. The pad segments 56 and bridgingsegments 57 of the second sensing electrodes 31 may have the samerespective shapes and widths as the first sensing electrodes 10. Eachseparated common electrode 108 may include several pad segments 109evenly spaced in the second direction y and connected to one another inthe second direction y by relatively narrow bridging segments 110. Thepad segments 109 and bridging segments 110 of the separated commonelectrodes 108 may have the same respective shapes and widths as thefirst and second sensing electrodes 10, 31. Alternatively, the padsegments 54 of the first sensing electrodes 10 may be larger or smallerthan the pad segments 109 of the separated common electrodes 108.

The first sensing electrodes 10 and the second sensing electrodes 31 arearranged such that the bridging segments 57 of the second sensingelectrodes 31 overlie the bridging segments 55 of the first sensingelectrodes 10. The first sensing electrodes 10 and the second sensingelectrodes 31 are arranged such that the respective pad segments 54, 56do not overlap. Instead, the separated common electrodes 108 arearranged such that the pad segments 109 of the separated commonelectrodes 108 overlap the pad segments 54 of the first sensingelectrodes 8. The pad segments 54, 56, 109 need not be diamond shaped,and may instead be circular. The pad segments 54, 56, 109 may be aregular polygon such as a triangle, square, pentagon or hexagon.

The fifth touch panel 107 may be used in, for example, the first touchpanel system 47 to measure mutual capacitance between a pair of firstand second sensing electrodes 10, 31. The separated common electrodes108 may be coupled to each another, for example using external traces(not shown) and addressed collectively to measure pressure valuesbetween each first sensing electrode 10 and the separated commonelectrodes 108. Alternatively, the separated common electrodes 108 maybe individually addressable to measure pressure values using a pair offirst and separated common electrodes 10, 108.

The first to eighth display stack ups 82, 85, 87, 88, 90, 92, 94, 95 orthe first to eighth embedded stack-ups 96, 100, 101, 102, 103, 104, 105,106 may be adapted to incorporate the fifth touch panel 107, or elementsof the fifth touch panel 107 such as, for example, disposing the secondsensing electrodes 31 on the same surface as the separated commonelectrodes 108. The separated common electrodes 108 need not be disposedon the same surface as the second sensing electrodes 31, and mayalternatively be disposed on the same surface of the layer structure 7as the first sensing electrodes 10.

Touch panels and stack-ups have been described which are generallyplanar. However, touch panels and stack-ups need not be planar or flatand may provide curved or other non-planar surfaces for a user tointeract with. Touch panels and stack-ups may be provided overlying orembedded within curved displays.

The pressure signal processing module 6, capacitive touch controller 5and/or the processor 37 may employ correlated double sampling methods toimprove the signal to noise ratio of the pressure values 24 and/or thecapacitance values 23. The pressure signal processing module 6,capacitive touch controller 5 and/or the processer 37 may process thepressure values 24 and/or the capacitance values 23 as image data.

Touch sensors 4, 26 and touch panels 36, 53, 58, 80 have been generallydescribed in relation to first, second and third (thickness) directionsx, y, z forming an orthogonal set. However, the first and seconddirections need not be perpendicular and may in general intersect at anyangle between 1 degree and 90 degrees, intersection of the first andsecond directions at 90, 60, 45 or 30 degrees is preferred.

Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure of the present invention also includes any novel features orany novel combination of features disclosed herein either explicitly orimplicitly or any generalization thereof, whether or not it relates tothe same invention as presently claimed in any claim and whether or notit mitigates any or all of the same technical problems as does thepresent invention. The applicant hereby gives notice that new claims maybe formulated to such features and: or combinations of such featuresduring the prosecution of the present application or of any furtherapplication derived therefrom.

What is claimed is:
 1. A device comprising: a plurality of firstinput/output terminals for a projected capacitance touch panel, whereinthe projected capacitance touch panel comprises a layer of piezoelectricmaterial disposed between a plurality of sensing electrodes and a commonelectrode; a plurality of second input/output terminals liar acapacitive touch controller; a plurality of separation stages, eachseparation stage connecting one first input/output terminal to acorresponding second input/output terminal, and each separation stagecomprising a first frequency-dependent filter for filtering signalsbetween respective first and second input/output terminals; at least oneamplification stage, each amplification stage having at least one inputand an output configured to provide an amplified signal, wherein thenumber of amplification stages is less than or equal to the number ofseparation stages and each amplification stage input is connected to oneor more of the first input/output terminals through the respectiveseparation stage(s): wherein each amplification stage or each separationstage comprises a second frequency-dependent filter for filteringsignals between the respective first input/output terminal and anamplification stage input; wherein each first frequency-dependent filteris configured to pass signals from the capacitive touch controller andeach second frequency-dependent filter is configured to attenuatesignals from the capacitive touch controller.
 2. A device according toclaim 1, wherein the second frequency-dependent filters are configuredsuch that the amplitude of the amplified signal from each amplificationstage output is dependent upon a pressure applied to the projectedcapacitance touch panel proximate to the sensing electrode(s) connectedto the corresponding first input/output terminal(s).
 3. A deviceaccording to claim 1, wherein each amplification stage is connected toone first input/output terminal through one separation stage.
 4. Adevice according to claim 1, wherein each amplification stage isconnected to a two or more of the first input/output terminals throughrespective separation stages.
 5. A device according to claim 1, whereinthe plurality of separation stages and the plurality of amplificationstages are connected by a resistance network.
 6. A device according toclaim further comprising: a common terminal for receiving bias signalsfrom the capacitive touch controller; wherein each separation stagefurther comprises an additional first frequency-dependent filter, and areference resistance and a reference capacitance connected in series,each separation stage configured to connect the respective secondinput/output terminal to the common terminal through the referenceresistance and capacitance, the additional first frequency-dependentfilter for filtering signals between the respective second input/outputterminal and the common terminal; wherein each amplification stage is adifferential amplification stage having a first amplification stageinput connected to one or more of the first input/output terminalsthrough the respective separation stage(s) and a second amplificationstage input connected to the common terminal through the referenceresistance and reference capacitance of the respective separationstage(s); wherein in dependence upon each separation stage including asecond frequency-dependent filter, each separation stage furthercomprises an additional second frequency-dependent filter for filteringsignals between the respective second amplification stage input firstterminal and the common terminal.
 7. A device according to claim 1,wherein each amplification stage comprises a second frequency-dependentfilter, and each second frequency dependent filter comprises a feedbacknetwork(s) and one or more operational amplifiers.
 8. A device accordingto claim 1, further comprising: a third terminal; and a pressure signalprocessing module having a plurality of inputs and an output, each inputconnected to a corresponding amplification stage output, and the outputconnected to the third terminal; wherein the pressure signal processingmodule is configured to receive the amplified signals, to calculatepressure values in dependence upon the amplified signals, and to providean output comprising pressure values to the third terminal.
 9. A deviceaccording to claim 1, further comprising: a capacitive touch controllerhaving a plurality of electrode monitoring ports and a common outputport, each electrode monitoring port connected to a corresponding secondinput/output terminal, and the common output port for providing biassignals to a common electrode of the projected capacitance touch panel;wherein the capacitive touch controller is configured to send and/orreceive signals to and/or from sensing electrodes of the projectedcapacitance touch panel via the respective signal separation stages, tocalculate capacitance values in dependence upon the sent and/or receivedsignals, and to provide an output comprising capacitance values. 10.Apparatus comprising: a device according to claim 1, the device furthercomprising a plurality of third terminals, each third terminal connectedto a corresponding amplification stage output; a pressure signalprocessing module having a plurality of inputs and an output, each inputconnected to a corresponding third terminal of the device; wherein thepressure signal processing module is configured to receive the amplifiedsignals, to calculate pressure values in dependence upon the amplifiedsignals, and to provide an output comprising pressure values. 11.Apparatus comprising: a device according to claim 1; and a capacitivetouch controller having a plurality of electrode monitoring ports and acommon output port, each electrode monitoring port connected to acorresponding second input/output terminal of the device, and the commonoutput port for providing bias signals to a common electrode of theprojected capacitance touch panel; wherein the capacitive touchcontroller is configured to send and/or receive signals to and/or fromsensing electrodes of the projected capacitance touch panel via therespective signal separation stages, to calculate capacitance values independence upon the sent and/or received signals, and to provide anoutput comprising capacitance values.
 12. A touch panel systemcomprising: a device according to claim 1; and a touch panel comprising:a layer structure comprising one or more layers, each layer extendingperpendicularly to a thickness direction, the one or more layersincluding a layer of piezoelectric material, the layer structure havingfirst and second opposite faces, and the layer(s) arranged between thefirst and second faces such that the thickness direction of each layeris perpendicular to the first and second faces; a plurality of firstsensing electrodes disposed on the first face, each first sensingelectrode connected to a corresponding first input/output terminal; anda common electrode disposed on the second face for receiving a biassignal from a capacitive touch controller; wherein in dependence uponthe device or the apparatus including a common terminal, the commonelectrode is connected to the common terminal, wherein in dependence onthe device or the apparatus including a capacitive touch controller, thecommon output port of the capacitive touch controller is connected tothe common electrode.
 13. A touch panel system according to claim 12,wherein the common electrode comprises a region of conductive materialarranged in a grid.
 14. A touch panel system according to claim 12,wherein the plurality of first electrodes comprises a plurality ofconductive pads disposed on the first face in an array.
 15. A touchpanel system according to claim 12, wherein the touch panel furthercomprises a plurality of second sensing electrodes disposed overlyingthe first face of the layer structure and arranged such that the layerstructure is between the plurality of second sensing electrodes and thecommon electrode; wherein each of second sensing electrodes is connectedto a corresponding first input/output terminal.
 16. A touch panel systemaccording to claim 15, wherein each first sensing electrode extends in afirst direction and the plurality of first sensing electrodes arearrayed spaced apart perpendicular to the first direction, and whereineach second sensing electrode extends in a second direction and theplurality of second sensing electrodes are arrayed spaced apartperpendicular to the second direction, wherein the first and seconddirections are different.
 17. A touch panel system according to claim15, wherein the touch panel further comprises a second layer structurecomprising one or more dielectric layers, each dielectric layerextending perpendicularly to a thickness direction, the second layerstructure having third and fourth opposite faces, the dielectric layersarranged between the third and fourth faces such that the thicknessdirection of each dielectric layer is perpendicular to the third andfourth faces; wherein the plurality of second sensing electrodes aredisposed on the third face of the second layer structure and the fourthface of the second layer structure contacts the plurality of firstsensing electrodes.
 18. A touch panel system according to claim 15,wherein the plurality of second sensing electrodes are disposed on thefirst thee of the layer structure, wherein each first sensing electrodecomprises a continuous conductive region and each second sensingelectrode comprises a plurality of conductive regions electricallyconnected to one another by jumpers, each jumper spanning a conductiveregion forming a portion of one of the first sensing electrodes.
 19. Aportable electronic device comprising: a device according to claim 1;and a signal processor arranged to receive the pressure values and/orcapacitance values, wherein the signal processor is configured to employcorrelated double sampling methods so as to improve signal to noiseratio of the pressure values and/or capacitance values.
 20. A methodcomprising: transmitting and filtering, using a firstfrequency-dependent filter, signals between a capacitive touchcontroller and a sensing electrode of a projected capacitance touchpanel which comprises a layer of piezoelectric material disposed betweena plurality of sensing electrodes and a common electrode; filtering,using a second frequency-dependent filter, signals between the sensingelectrode of the projected capacitance touch panel and an amplificationstage input to produce a filtered signal; and amplifying the filteredsignal to produce an amplified signal; wherein each firstfrequency-dependent filter is configured to pass signals from thecapacitive touch controller and each second frequency-dependent filteris configured to attenuate signals from the capacitive touch controller